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Revert "[X86] Promote cttz_i32(x) -> cttz_i64((i64)x | (1 << 32))" #103030

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Merged
merged 1 commit into from
Aug 13, 2024
Merged

Revert "[X86] Promote cttz_i32(x) -> cttz_i64((i64)x | (1 << 32))" #103030

merged 1 commit into from
Aug 13, 2024

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@RKSimon RKSimon commented Aug 13, 2024

Reverts #102900 - missed a analysis cost model test change

@RKSimon RKSimon merged commit 346a1c5 into main Aug 13, 2024
@RKSimon RKSimon deleted the revert-102900-x86-promote-cttz-i32 branch August 13, 2024 09:30
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llvmbot commented Aug 13, 2024

@llvm/pr-subscribers-backend-x86

Author: Simon Pilgrim (RKSimon)

Changes

Reverts llvm/llvm-project#102900 - missed a analysis cost model test change

Patch is 24.89 KiB, truncated to 20.00 KiB below, full version: https://github.com/llvm/llvm-project/pull/103030.diff

5 Files Affected:

  • (modified) llvm/lib/Target/X86/X86ISelLowering.cpp (+2-4)
  • (modified) llvm/test/CodeGen/X86/cttz.ll (+7-5)
  • (modified) llvm/test/CodeGen/X86/known-never-zero.ll (+207-132)
  • (modified) llvm/test/CodeGen/X86/pr89877.ll (+8-5)
  • (modified) llvm/test/CodeGen/X86/pr90847.ll (+16-8)
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
index 04dfd0ea0d893a..2074fac8578914 100644
--- a/llvm/lib/Target/X86/X86ISelLowering.cpp
+++ b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -412,7 +412,6 @@ X86TargetLowering::X86TargetLowering(const X86TargetMachine &TM,
     setOperationAction(ISD::CTTZ           , MVT::i32  , Custom);
     setOperationAction(ISD::CTTZ_ZERO_UNDEF, MVT::i32  , Legal);
     if (Subtarget.is64Bit()) {
-      setOperationPromotedToType(ISD::CTTZ , MVT::i32, MVT::i64);
       setOperationAction(ISD::CTTZ         , MVT::i64  , Custom);
       setOperationAction(ISD::CTTZ_ZERO_UNDEF, MVT::i64, Legal);
     }
@@ -3238,10 +3237,9 @@ bool X86TargetLowering::shouldFormOverflowOp(unsigned Opcode, EVT VT,
 }
 
 bool X86TargetLowering::isCheapToSpeculateCttz(Type *Ty) const {
-  // Speculate cttz only if we can directly use TZCNT or can promote to i32/i64.
+  // Speculate cttz only if we can directly use TZCNT or can promote to i32.
   return Subtarget.hasBMI() ||
-         (!Ty->isVectorTy() &&
-          Ty->getScalarSizeInBits() < (Subtarget.is64Bit() ? 64u : 32u));
+         (!Ty->isVectorTy() && Ty->getScalarSizeInBits() < 32);
 }
 
 bool X86TargetLowering::isCheapToSpeculateCtlz(Type *Ty) const {
diff --git a/llvm/test/CodeGen/X86/cttz.ll b/llvm/test/CodeGen/X86/cttz.ll
index b35a1b72fcb6f1..6eb748a1afbab5 100644
--- a/llvm/test/CodeGen/X86/cttz.ll
+++ b/llvm/test/CodeGen/X86/cttz.ll
@@ -317,11 +317,13 @@ define i32 @cttz_i32_zero_test(i32 %n) {
 ;
 ; X64-LABEL: cttz_i32_zero_test:
 ; X64:       # %bb.0:
-; X64-NEXT:    # kill: def $edi killed $edi def $rdi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rdi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %edi, %edi
+; X64-NEXT:    je .LBB6_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %edi, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB6_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
 ;
 ; X86-CLZ-LABEL: cttz_i32_zero_test:
diff --git a/llvm/test/CodeGen/X86/known-never-zero.ll b/llvm/test/CodeGen/X86/known-never-zero.ll
index d5d604a138a719..df11a44626e381 100644
--- a/llvm/test/CodeGen/X86/known-never-zero.ll
+++ b/llvm/test/CodeGen/X86/known-never-zero.ll
@@ -54,12 +54,13 @@ define i32 @or_maybe_zero(i32 %x, i32 %y) {
 ;
 ; X64-LABEL: or_maybe_zero:
 ; X64:       # %bb.0:
-; X64-NEXT:    # kill: def $edi killed $edi def $rdi
 ; X64-NEXT:    orl %esi, %edi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rdi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    je .LBB1_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %edi, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB1_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = or i32 %x, %y
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -114,10 +115,13 @@ define i32 @select_maybe_zero(i1 %c, i32 %x) {
 ; X64-NEXT:    xorl %eax, %eax
 ; X64-NEXT:    testb $1, %dil
 ; X64-NEXT:    cmovnel %esi, %eax
-; X64-NEXT:    movabsq $4294967296, %rcx # imm = 0x100000000
-; X64-NEXT:    orq %rax, %rcx
-; X64-NEXT:    rep bsfq %rcx, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %eax, %eax
+; X64-NEXT:    je .LBB3_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB3_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %y = or i32 %x, 1
   %z = select i1 %c, i32 %y, i32 0
@@ -212,14 +216,16 @@ define i32 @shl_maybe_zero(i32 %x, i32 %y) {
 ;
 ; X64-LABEL: shl_maybe_zero:
 ; X64:       # %bb.0:
-; X64-NEXT:    # kill: def $esi killed $esi def $rsi
 ; X64-NEXT:    movl %edi, %ecx
 ; X64-NEXT:    # kill: def $cl killed $cl killed $ecx
 ; X64-NEXT:    shll %cl, %esi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rsi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %esi, %esi
+; X64-NEXT:    je .LBB7_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %esi, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB7_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = shl nuw nsw i32 %y, %x
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -269,10 +275,13 @@ define i32 @uaddsat_maybe_zero(i32 %x, i32 %y) {
 ; X64-NEXT:    addl %esi, %edi
 ; X64-NEXT:    movl $-1, %eax
 ; X64-NEXT:    cmovael %edi, %eax
-; X64-NEXT:    movabsq $4294967296, %rcx # imm = 0x100000000
-; X64-NEXT:    orq %rax, %rcx
-; X64-NEXT:    rep bsfq %rcx, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %eax, %eax
+; X64-NEXT:    je .LBB9_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB9_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = call i32 @llvm.uadd.sat.i32(i32 %x, i32 %y)
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -325,13 +334,15 @@ define i32 @umax_maybe_zero(i32 %x, i32 %y) {
 ;
 ; X64-LABEL: umax_maybe_zero:
 ; X64:       # %bb.0:
-; X64-NEXT:    # kill: def $esi killed $esi def $rsi
 ; X64-NEXT:    cmpl %esi, %edi
 ; X64-NEXT:    cmoval %edi, %esi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rsi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %esi, %esi
+; X64-NEXT:    je .LBB11_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %esi, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB11_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = call i32 @llvm.umax.i32(i32 %x, i32 %y)
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -390,10 +401,13 @@ define i32 @umin_maybe_zero(i32 %x, i32 %y) {
 ; X64-NEXT:    cmpl $54, %edi
 ; X64-NEXT:    movl $54, %eax
 ; X64-NEXT:    cmovbl %edi, %eax
-; X64-NEXT:    movabsq $4294967296, %rcx # imm = 0x100000000
-; X64-NEXT:    orq %rax, %rcx
-; X64-NEXT:    rep bsfq %rcx, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %eax, %eax
+; X64-NEXT:    je .LBB13_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB13_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = call i32 @llvm.umin.i32(i32 %x, i32 54)
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -508,10 +522,13 @@ define i32 @smin_maybe_zero(i32 %x, i32 %y) {
 ; X64-NEXT:    cmpl $54, %edi
 ; X64-NEXT:    movl $54, %eax
 ; X64-NEXT:    cmovll %edi, %eax
-; X64-NEXT:    movabsq $4294967296, %rcx # imm = 0x100000000
-; X64-NEXT:    orq %rax, %rcx
-; X64-NEXT:    rep bsfq %rcx, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %eax, %eax
+; X64-NEXT:    je .LBB17_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB17_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = call i32 @llvm.smin.i32(i32 %x, i32 54)
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -626,10 +643,13 @@ define i32 @smax_known_zero(i32 %x, i32 %y) {
 ; X64-NEXT:    testl %edi, %edi
 ; X64-NEXT:    movl $-1, %eax
 ; X64-NEXT:    cmovnsl %edi, %eax
-; X64-NEXT:    movabsq $4294967296, %rcx # imm = 0x100000000
-; X64-NEXT:    orq %rax, %rcx
-; X64-NEXT:    rep bsfq %rcx, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %eax, %eax
+; X64-NEXT:    je .LBB21_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB21_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = call i32 @llvm.smax.i32(i32 %x, i32 -1)
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -656,9 +676,16 @@ define i32 @rotr_known_nonzero(i32 %xx, i32 %y) {
 ; X64:       # %bb.0:
 ; X64-NEXT:    movl %esi, %ecx
 ; X64-NEXT:    orl $256, %edi # imm = 0x100
+; X64-NEXT:    movl %edi, %eax
 ; X64-NEXT:    # kill: def $cl killed $cl killed $ecx
-; X64-NEXT:    rorl %cl, %edi
-; X64-NEXT:    rep bsfl %edi, %eax
+; X64-NEXT:    rorl %cl, %eax
+; X64-NEXT:    testl %edi, %edi
+; X64-NEXT:    je .LBB22_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB22_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %x = or i32 %xx, 256
   %shr = lshr i32 %x, %y
@@ -687,13 +714,16 @@ define i32 @rotr_maybe_zero(i32 %x, i32 %y) {
 ; X64-LABEL: rotr_maybe_zero:
 ; X64:       # %bb.0:
 ; X64-NEXT:    movl %esi, %ecx
-; X64-NEXT:    # kill: def $edi killed $edi def $rdi
+; X64-NEXT:    movl %edi, %eax
 ; X64-NEXT:    # kill: def $cl killed $cl killed $ecx
-; X64-NEXT:    rorl %cl, %edi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rdi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    rorl %cl, %eax
+; X64-NEXT:    testl %edi, %edi
+; X64-NEXT:    je .LBB23_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB23_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %shr = lshr i32 %x, %y
   %sub = sub i32 32, %y
@@ -745,13 +775,16 @@ define i32 @rotr_with_fshr_maybe_zero(i32 %x, i32 %y) {
 ; X64-LABEL: rotr_with_fshr_maybe_zero:
 ; X64:       # %bb.0:
 ; X64-NEXT:    movl %esi, %ecx
-; X64-NEXT:    # kill: def $edi killed $edi def $rdi
+; X64-NEXT:    movl %edi, %eax
 ; X64-NEXT:    # kill: def $cl killed $cl killed $ecx
-; X64-NEXT:    rorl %cl, %edi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rdi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    rorl %cl, %eax
+; X64-NEXT:    testl %edi, %edi
+; X64-NEXT:    je .LBB25_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB25_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = call i32 @llvm.fshr.i32(i32 %x, i32 %x, i32 %y)
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -778,9 +811,16 @@ define i32 @rotl_known_nonzero(i32 %xx, i32 %y) {
 ; X64:       # %bb.0:
 ; X64-NEXT:    movl %esi, %ecx
 ; X64-NEXT:    orl $256, %edi # imm = 0x100
+; X64-NEXT:    movl %edi, %eax
 ; X64-NEXT:    # kill: def $cl killed $cl killed $ecx
-; X64-NEXT:    roll %cl, %edi
-; X64-NEXT:    rep bsfl %edi, %eax
+; X64-NEXT:    roll %cl, %eax
+; X64-NEXT:    testl %edi, %edi
+; X64-NEXT:    je .LBB26_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB26_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %x = or i32 %xx, 256
   %shl = shl i32 %x, %y
@@ -809,13 +849,16 @@ define i32 @rotl_maybe_zero(i32 %x, i32 %y) {
 ; X64-LABEL: rotl_maybe_zero:
 ; X64:       # %bb.0:
 ; X64-NEXT:    movl %esi, %ecx
-; X64-NEXT:    # kill: def $edi killed $edi def $rdi
+; X64-NEXT:    movl %edi, %eax
 ; X64-NEXT:    # kill: def $cl killed $cl killed $ecx
-; X64-NEXT:    roll %cl, %edi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rdi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    roll %cl, %eax
+; X64-NEXT:    testl %edi, %edi
+; X64-NEXT:    je .LBB27_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB27_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %shl = shl i32 %x, %y
   %sub = sub i32 32, %y
@@ -867,13 +910,16 @@ define i32 @rotl_with_fshl_maybe_zero(i32 %x, i32 %y) {
 ; X64-LABEL: rotl_with_fshl_maybe_zero:
 ; X64:       # %bb.0:
 ; X64-NEXT:    movl %esi, %ecx
-; X64-NEXT:    # kill: def $edi killed $edi def $rdi
+; X64-NEXT:    movl %edi, %eax
 ; X64-NEXT:    # kill: def $cl killed $cl killed $ecx
-; X64-NEXT:    roll %cl, %edi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rdi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    roll %cl, %eax
+; X64-NEXT:    testl %edi, %edi
+; X64-NEXT:    je .LBB29_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB29_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = call i32 @llvm.fshl.i32(i32 %x, i32 %x, i32 %y)
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -943,14 +989,16 @@ define i32 @sra_maybe_zero(i32 %x, i32 %y) {
 ;
 ; X64-LABEL: sra_maybe_zero:
 ; X64:       # %bb.0:
-; X64-NEXT:    # kill: def $esi killed $esi def $rsi
 ; X64-NEXT:    movl %edi, %ecx
 ; X64-NEXT:    # kill: def $cl killed $cl killed $ecx
 ; X64-NEXT:    sarl %cl, %esi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rsi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %esi, %esi
+; X64-NEXT:    je .LBB32_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %esi, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB32_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = ashr exact i32 %y, %x
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -1020,14 +1068,16 @@ define i32 @srl_maybe_zero(i32 %x, i32 %y) {
 ;
 ; X64-LABEL: srl_maybe_zero:
 ; X64:       # %bb.0:
-; X64-NEXT:    # kill: def $esi killed $esi def $rsi
 ; X64-NEXT:    movl %edi, %ecx
 ; X64-NEXT:    # kill: def $cl killed $cl killed $ecx
 ; X64-NEXT:    shrl %cl, %esi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rsi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %esi, %esi
+; X64-NEXT:    je .LBB35_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %esi, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB35_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = lshr exact i32 %y, %x
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -1078,11 +1128,13 @@ define i32 @udiv_maybe_zero(i32 %x, i32 %y) {
 ; X64-NEXT:    movl %edi, %eax
 ; X64-NEXT:    xorl %edx, %edx
 ; X64-NEXT:    divl %esi
-; X64-NEXT:    # kill: def $eax killed $eax def $rax
-; X64-NEXT:    movabsq $4294967296, %rcx # imm = 0x100000000
-; X64-NEXT:    orq %rax, %rcx
-; X64-NEXT:    rep bsfq %rcx, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %eax, %eax
+; X64-NEXT:    je .LBB37_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB37_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = udiv exact i32 %x, %y
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -1133,11 +1185,13 @@ define i32 @sdiv_maybe_zero(i32 %x, i32 %y) {
 ; X64-NEXT:    movl %edi, %eax
 ; X64-NEXT:    cltd
 ; X64-NEXT:    idivl %esi
-; X64-NEXT:    # kill: def $eax killed $eax def $rax
-; X64-NEXT:    movabsq $4294967296, %rcx # imm = 0x100000000
-; X64-NEXT:    orq %rax, %rcx
-; X64-NEXT:    rep bsfq %rcx, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %eax, %eax
+; X64-NEXT:    je .LBB39_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB39_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = sdiv exact i32 %x, %y
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -1181,13 +1235,14 @@ define i32 @add_maybe_zero(i32 %xx, i32 %y) {
 ;
 ; X64-LABEL: add_maybe_zero:
 ; X64:       # %bb.0:
-; X64-NEXT:    # kill: def $edi killed $edi def $rdi
 ; X64-NEXT:    orl $1, %edi
 ; X64-NEXT:    addl %esi, %edi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rdi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    je .LBB41_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %edi, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB41_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %x = or i32 %xx, 1
   %z = add nsw i32 %x, %y
@@ -1266,10 +1321,12 @@ define i32 @sub_maybe_zero(i32 %x) {
 ; X64-NEXT:    movl %edi, %eax
 ; X64-NEXT:    orl $64, %eax
 ; X64-NEXT:    subl %edi, %eax
-; X64-NEXT:    movabsq $4294967296, %rcx # imm = 0x100000000
-; X64-NEXT:    orq %rax, %rcx
-; X64-NEXT:    rep bsfq %rcx, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    je .LBB44_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %eax, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB44_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %y = or i32 %x, 64
   %z = sub i32 %y, %x
@@ -1292,12 +1349,13 @@ define i32 @sub_maybe_zero2(i32 %x) {
 ;
 ; X64-LABEL: sub_maybe_zero2:
 ; X64:       # %bb.0:
-; X64-NEXT:    # kill: def $edi killed $edi def $rdi
 ; X64-NEXT:    negl %edi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rdi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    je .LBB45_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %edi, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB45_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = sub i32 0, %x
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -1321,13 +1379,15 @@ define i32 @mul_known_nonzero_nsw(i32 %x, i32 %yy) {
 ;
 ; X64-LABEL: mul_known_nonzero_nsw:
 ; X64:       # %bb.0:
-; X64-NEXT:    # kill: def $esi killed $esi def $rsi
 ; X64-NEXT:    orl $256, %esi # imm = 0x100
 ; X64-NEXT:    imull %edi, %esi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rsi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %esi, %esi
+; X64-NEXT:    je .LBB46_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %esi, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB46_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %y = or i32 %yy, 256
   %z = mul nsw i32 %y, %x
@@ -1352,13 +1412,15 @@ define i32 @mul_known_nonzero_nuw(i32 %x, i32 %yy) {
 ;
 ; X64-LABEL: mul_known_nonzero_nuw:
 ; X64:       # %bb.0:
-; X64-NEXT:    # kill: def $esi killed $esi def $rsi
 ; X64-NEXT:    orl $256, %esi # imm = 0x100
 ; X64-NEXT:    imull %edi, %esi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rsi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %esi, %esi
+; X64-NEXT:    je .LBB47_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %esi, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB47_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %y = or i32 %yy, 256
   %z = mul nuw i32 %y, %x
@@ -1382,12 +1444,14 @@ define i32 @mul_maybe_zero(i32 %x, i32 %y) {
 ;
 ; X64-LABEL: mul_maybe_zero:
 ; X64:       # %bb.0:
-; X64-NEXT:    # kill: def $edi killed $edi def $rdi
 ; X64-NEXT:    imull %esi, %edi
-; X64-NEXT:    movabsq $4294967296, %rax # imm = 0x100000000
-; X64-NEXT:    orq %rdi, %rax
-; X64-NEXT:    rep bsfq %rax, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    testl %edi, %edi
+; X64-NEXT:    je .LBB48_1
+; X64-NEXT:  # %bb.2: # %cond.false
+; X64-NEXT:    rep bsfl %edi, %eax
+; X64-NEXT:    retq
+; X64-NEXT:  .LBB48_1:
+; X64-NEXT:    movl $32, %eax
 ; X64-NEXT:    retq
   %z = mul nuw nsw i32 %y, %x
   %r = call i32 @llvm.cttz.i32(i32 %z, i1 false)
@@ -1418,10 +1482,9 @@ define i32 @bitcast_known_nonzero(<2 x i16> %xx) {
 ; X64-NEXT:    vpackusdw %xmm0, %xmm0, %xmm0
 ; X64-NEXT:    vpmullw {{\.?LCPI[0-9]+_[0-9]+}}(%rip), %xmm0, %xmm0 # [256,256,u,u,u,u,u,u]
 ; X64-NEXT:    vmovd %xmm0, %eax
-; X64-NEXT:    movabsq $4294967296, %rcx # imm = 0x100000000
-; X64-NEXT:    orq %rax, %rcx
-; X64-NEXT:    rep bsfq %rcx, %rax
-; X64-NEXT:    # kill: def $eax killed $eax killed $rax
+; X64-NEXT:    bsfl %eax, %ecx
+; X64-NEXT:    movl $32, %eax
+; X64-NEXT:    cmovnel %ecx, %eax
 ; X64-NEXT:    retq
   %x = shl nuw nsw <2 x i16> <i16 256, i16 256>, %xx
   %z = bitcast <2 x i16> %x to i32
@@ -1445,10 +1508,13 @@ define i32 @bitcast_maybe_zero(<2 x i16> %x) {
 ; X64-LABEL: bitcas...
[truncated]

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@RKSimon @llvmbot