release/21.x: [X86] Use pseudo instructions to zero registers in `buildClearRegister` (#163358) #164076

llvmbot · 2025-10-18T11:46:07Z

Backport 228dae7

Requested by: @RKSimon

llvmbot · 2025-10-18T11:46:14Z

@RKSimon What do you think about merging this PR to the release branch?

llvmbot · 2025-10-18T11:46:36Z

@llvm/pr-subscribers-backend-x86

Author: None (llvmbot)

Changes

Backport 228dae7

Requested by: @RKSimon

Full diff: https://github.com/llvm/llvm-project/pull/164076.diff

2 Files Affected:

(modified) llvm/lib/Target/X86/X86InstrInfo.cpp (+5-17)
(added) llvm/test/CodeGen/X86/zero-call-used-regs-simd.ll (+216)

diff --git a/llvm/lib/Target/X86/X86InstrInfo.cpp b/llvm/lib/Target/X86/X86InstrInfo.cpp
index abf365eedec39..9bf58dd3458cd 100644
--- a/llvm/lib/Target/X86/X86InstrInfo.cpp
+++ b/llvm/lib/Target/X86/X86InstrInfo.cpp
@@ -10739,39 +10739,27 @@ void X86InstrInfo::buildClearRegister(Register Reg, MachineBasicBlock &MBB,
     if (!ST.hasSSE1())
       return;
 
-    // PXOR is safe to use because it doesn't affect flags.
-    BuildMI(MBB, Iter, DL, get(X86::PXORrr), Reg)
-        .addReg(Reg, RegState::Undef)
-        .addReg(Reg, RegState::Undef);
+    BuildMI(MBB, Iter, DL, get(X86::V_SET0), Reg);
   } else if (X86::VR256RegClass.contains(Reg)) {
     // YMM#
     if (!ST.hasAVX())
       return;
 
-    // VPXOR is safe to use because it doesn't affect flags.
-    BuildMI(MBB, Iter, DL, get(X86::VPXORrr), Reg)
-        .addReg(Reg, RegState::Undef)
-        .addReg(Reg, RegState::Undef);
+    BuildMI(MBB, Iter, DL, get(X86::AVX_SET0), Reg);
   } else if (X86::VR512RegClass.contains(Reg)) {
     // ZMM#
     if (!ST.hasAVX512())
       return;
 
-    // VPXORY is safe to use because it doesn't affect flags.
-    BuildMI(MBB, Iter, DL, get(X86::VPXORYrr), Reg)
-        .addReg(Reg, RegState::Undef)
-        .addReg(Reg, RegState::Undef);
+    BuildMI(MBB, Iter, DL, get(X86::AVX512_512_SET0), Reg);
   } else if (X86::VK1RegClass.contains(Reg) || X86::VK2RegClass.contains(Reg) ||
              X86::VK4RegClass.contains(Reg) || X86::VK8RegClass.contains(Reg) ||
              X86::VK16RegClass.contains(Reg)) {
     if (!ST.hasVLX())
       return;
 
-    // KXOR is safe to use because it doesn't affect flags.
-    unsigned Op = ST.hasBWI() ? X86::KXORQkk : X86::KXORWkk;
-    BuildMI(MBB, Iter, DL, get(Op), Reg)
-        .addReg(Reg, RegState::Undef)
-        .addReg(Reg, RegState::Undef);
+    unsigned Op = ST.hasBWI() ? X86::KSET0Q : X86::KSET0W;
+    BuildMI(MBB, Iter, DL, get(Op), Reg);
   }
 }
 
diff --git a/llvm/test/CodeGen/X86/zero-call-used-regs-simd.ll b/llvm/test/CodeGen/X86/zero-call-used-regs-simd.ll
new file mode 100644
index 0000000000000..d9253e0ca127b
--- /dev/null
+++ b/llvm/test/CodeGen/X86/zero-call-used-regs-simd.ll
@@ -0,0 +1,216 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
+; RUN: llc < %s -mtriple=x86_64-- -mattr=+sse2                        -verify-machineinstrs | FileCheck %s --check-prefixes=SSE
+; RUN: llc < %s -mtriple=x86_64-- -mattr=+avx                         -verify-machineinstrs | FileCheck %s --check-prefixes=AVX,AVX1
+; RUN: llc < %s -mtriple=x86_64-- -mattr=+avx2                        -verify-machineinstrs | FileCheck %s --check-prefixes=AVX,AVX2
+; RUN: llc < %s -mtriple=x86_64-- -mattr=+avx512f,+avx512vl           -verify-machineinstrs | FileCheck %s --check-prefixes=AVX512,AVX512VL
+; RUN: llc < %s -mtriple=x86_64-- -mattr=+avx512f,+avx512vl,+avx512bw -verify-machineinstrs | FileCheck %s --check-prefixes=AVX512,AVX512BW
+
+define void @zero_xmm(<4 x i32> %arg) #0 {
+; SSE-LABEL: zero_xmm:
+; SSE:       # %bb.0:
+; SSE-NEXT:    movaps %xmm0, 0
+; SSE-NEXT:    xorps %xmm0, %xmm0
+; SSE-NEXT:    retq
+;
+; AVX-LABEL: zero_xmm:
+; AVX:       # %bb.0:
+; AVX-NEXT:    vmovaps %xmm0, 0
+; AVX-NEXT:    vxorps %xmm0, %xmm0, %xmm0
+; AVX-NEXT:    retq
+;
+; AVX512-LABEL: zero_xmm:
+; AVX512:       # %bb.0:
+; AVX512-NEXT:    vmovaps %xmm0, 0
+; AVX512-NEXT:    vxorps %xmm0, %xmm0, %xmm0
+; AVX512-NEXT:    retq
+  store <4 x i32> %arg, ptr null, align 32
+  ret void
+}
+
+define void @zero_ymm(<8 x i32> %arg) #0 {
+; SSE-LABEL: zero_ymm:
+; SSE:       # %bb.0:
+; SSE-NEXT:    movaps %xmm1, 16
+; SSE-NEXT:    movaps %xmm0, 0
+; SSE-NEXT:    xorps %xmm0, %xmm0
+; SSE-NEXT:    xorps %xmm1, %xmm1
+; SSE-NEXT:    retq
+;
+; AVX-LABEL: zero_ymm:
+; AVX:       # %bb.0:
+; AVX-NEXT:    vmovaps %ymm0, 0
+; AVX-NEXT:    vxorps %xmm0, %xmm0, %xmm0
+; AVX-NEXT:    vzeroupper
+; AVX-NEXT:    retq
+;
+; AVX512-LABEL: zero_ymm:
+; AVX512:       # %bb.0:
+; AVX512-NEXT:    vmovaps %ymm0, 0
+; AVX512-NEXT:    vxorps %xmm0, %xmm0, %xmm0
+; AVX512-NEXT:    vzeroupper
+; AVX512-NEXT:    retq
+  store <8 x i32> %arg, ptr null, align 32
+  ret void
+}
+
+define void @zero_zmm(<16 x i32> %arg) #0 {
+; SSE-LABEL: zero_zmm:
+; SSE:       # %bb.0:
+; SSE-NEXT:    movaps %xmm3, 48
+; SSE-NEXT:    movaps %xmm2, 32
+; SSE-NEXT:    movaps %xmm1, 16
+; SSE-NEXT:    movaps %xmm0, 0
+; SSE-NEXT:    xorps %xmm0, %xmm0
+; SSE-NEXT:    xorps %xmm1, %xmm1
+; SSE-NEXT:    xorps %xmm2, %xmm2
+; SSE-NEXT:    xorps %xmm3, %xmm3
+; SSE-NEXT:    retq
+;
+; AVX-LABEL: zero_zmm:
+; AVX:       # %bb.0:
+; AVX-NEXT:    vmovaps %ymm1, 32
+; AVX-NEXT:    vmovaps %ymm0, 0
+; AVX-NEXT:    vxorps %xmm0, %xmm0, %xmm0
+; AVX-NEXT:    vxorps %xmm1, %xmm1, %xmm1
+; AVX-NEXT:    vzeroupper
+; AVX-NEXT:    retq
+;
+; AVX512-LABEL: zero_zmm:
+; AVX512:       # %bb.0:
+; AVX512-NEXT:    vmovups %zmm0, 0
+; AVX512-NEXT:    vxorps %xmm0, %xmm0, %xmm0
+; AVX512-NEXT:    vzeroupper
+; AVX512-NEXT:    retq
+  store <16 x i32> %arg, ptr null, align 32
+  ret void
+}
+
+define void @zero_k(<8 x i32> %arg, <8 x i1> %mask) #0 {
+; SSE-LABEL: zero_k:
+; SSE:       # %bb.0:
+; SSE-NEXT:    psllw $15, %xmm2
+; SSE-NEXT:    packsswb %xmm2, %xmm2
+; SSE-NEXT:    pmovmskb %xmm2, %eax
+; SSE-NEXT:    testb $1, %al
+; SSE-NEXT:    jne .LBB3_1
+; SSE-NEXT:  # %bb.2: # %else
+; SSE-NEXT:    testb $2, %al
+; SSE-NEXT:    jne .LBB3_3
+; SSE-NEXT:  .LBB3_4: # %else2
+; SSE-NEXT:    testb $4, %al
+; SSE-NEXT:    jne .LBB3_5
+; SSE-NEXT:  .LBB3_6: # %else4
+; SSE-NEXT:    testb $8, %al
+; SSE-NEXT:    jne .LBB3_7
+; SSE-NEXT:  .LBB3_8: # %else6
+; SSE-NEXT:    testb $16, %al
+; SSE-NEXT:    jne .LBB3_9
+; SSE-NEXT:  .LBB3_10: # %else8
+; SSE-NEXT:    testb $32, %al
+; SSE-NEXT:    jne .LBB3_11
+; SSE-NEXT:  .LBB3_12: # %else10
+; SSE-NEXT:    testb $64, %al
+; SSE-NEXT:    jne .LBB3_13
+; SSE-NEXT:  .LBB3_14: # %else12
+; SSE-NEXT:    testb $-128, %al
+; SSE-NEXT:    je .LBB3_16
+; SSE-NEXT:  .LBB3_15: # %cond.store13
+; SSE-NEXT:    pshufd {{.*#+}} xmm0 = xmm1[3,3,3,3]
+; SSE-NEXT:    movd %xmm0, 28
+; SSE-NEXT:  .LBB3_16: # %else14
+; SSE-NEXT:    xorl %eax, %eax
+; SSE-NEXT:    pxor %xmm0, %xmm0
+; SSE-NEXT:    pxor %xmm1, %xmm1
+; SSE-NEXT:    pxor %xmm2, %xmm2
+; SSE-NEXT:    retq
+; SSE-NEXT:  .LBB3_1: # %cond.store
+; SSE-NEXT:    movd %xmm0, 0
+; SSE-NEXT:    testb $2, %al
+; SSE-NEXT:    je .LBB3_4
+; SSE-NEXT:  .LBB3_3: # %cond.store1
+; SSE-NEXT:    pshufd {{.*#+}} xmm2 = xmm0[1,1,1,1]
+; SSE-NEXT:    movd %xmm2, 4
+; SSE-NEXT:    testb $4, %al
+; SSE-NEXT:    je .LBB3_6
+; SSE-NEXT:  .LBB3_5: # %cond.store3
+; SSE-NEXT:    pshufd {{.*#+}} xmm2 = xmm0[2,3,2,3]
+; SSE-NEXT:    movd %xmm2, 8
+; SSE-NEXT:    testb $8, %al
+; SSE-NEXT:    je .LBB3_8
+; SSE-NEXT:  .LBB3_7: # %cond.store5
+; SSE-NEXT:    pshufd {{.*#+}} xmm0 = xmm0[3,3,3,3]
+; SSE-NEXT:    movd %xmm0, 12
+; SSE-NEXT:    testb $16, %al
+; SSE-NEXT:    je .LBB3_10
+; SSE-NEXT:  .LBB3_9: # %cond.store7
+; SSE-NEXT:    movd %xmm1, 16
+; SSE-NEXT:    testb $32, %al
+; SSE-NEXT:    je .LBB3_12
+; SSE-NEXT:  .LBB3_11: # %cond.store9
+; SSE-NEXT:    pshufd {{.*#+}} xmm0 = xmm1[1,1,1,1]
+; SSE-NEXT:    movd %xmm0, 20
+; SSE-NEXT:    testb $64, %al
+; SSE-NEXT:    je .LBB3_14
+; SSE-NEXT:  .LBB3_13: # %cond.store11
+; SSE-NEXT:    pshufd {{.*#+}} xmm0 = xmm1[2,3,2,3]
+; SSE-NEXT:    movd %xmm0, 24
+; SSE-NEXT:    testb $-128, %al
+; SSE-NEXT:    jne .LBB3_15
+; SSE-NEXT:    jmp .LBB3_16
+;
+; AVX1-LABEL: zero_k:
+; AVX1:       # %bb.0:
+; AVX1-NEXT:    vpmovzxwd {{.*#+}} xmm2 = xmm1[0],zero,xmm1[1],zero,xmm1[2],zero,xmm1[3],zero
+; AVX1-NEXT:    vpslld $31, %xmm2, %xmm2
+; AVX1-NEXT:    vpunpckhwd {{.*#+}} xmm1 = xmm1[4,4,5,5,6,6,7,7]
+; AVX1-NEXT:    vpslld $31, %xmm1, %xmm1
+; AVX1-NEXT:    vinsertf128 $1, %xmm1, %ymm2, %ymm1
+; AVX1-NEXT:    vmaskmovps %ymm0, %ymm1, 0
+; AVX1-NEXT:    vxorps %xmm0, %xmm0, %xmm0
+; AVX1-NEXT:    vxorps %xmm1, %xmm1, %xmm1
+; AVX1-NEXT:    vpxor %xmm2, %xmm2, %xmm2
+; AVX1-NEXT:    vxorps %xmm0, %xmm0, %xmm0
+; AVX1-NEXT:    vxorps %xmm1, %xmm1, %xmm1
+; AVX1-NEXT:    vpxor %xmm2, %xmm2, %xmm2
+; AVX1-NEXT:    vzeroupper
+; AVX1-NEXT:    retq
+;
+; AVX2-LABEL: zero_k:
+; AVX2:       # %bb.0:
+; AVX2-NEXT:    vpmovzxwd {{.*#+}} ymm1 = xmm1[0],zero,xmm1[1],zero,xmm1[2],zero,xmm1[3],zero,xmm1[4],zero,xmm1[5],zero,xmm1[6],zero,xmm1[7],zero
+; AVX2-NEXT:    vpslld $31, %ymm1, %ymm1
+; AVX2-NEXT:    vpmaskmovd %ymm0, %ymm1, 0
+; AVX2-NEXT:    vpxor %xmm1, %xmm1, %xmm1
+; AVX2-NEXT:    vpxor %xmm0, %xmm0, %xmm0
+; AVX2-NEXT:    vpxor %xmm1, %xmm1, %xmm1
+; AVX2-NEXT:    vzeroupper
+; AVX2-NEXT:    retq
+;
+; AVX512VL-LABEL: zero_k:
+; AVX512VL:       # %bb.0:
+; AVX512VL-NEXT:    vpmovsxwd %xmm1, %ymm1
+; AVX512VL-NEXT:    vpslld $31, %ymm1, %ymm1
+; AVX512VL-NEXT:    vptestmd %ymm1, %ymm1, %k1
+; AVX512VL-NEXT:    vmovdqa32 %ymm0, 0 {%k1}
+; AVX512VL-NEXT:    vpxor %xmm1, %xmm1, %xmm1
+; AVX512VL-NEXT:    vpxor %xmm0, %xmm0, %xmm0
+; AVX512VL-NEXT:    vpxor %xmm1, %xmm1, %xmm1
+; AVX512VL-NEXT:    kxorw %k0, %k0, %k1
+; AVX512VL-NEXT:    vzeroupper
+; AVX512VL-NEXT:    retq
+;
+; AVX512BW-LABEL: zero_k:
+; AVX512BW:       # %bb.0:
+; AVX512BW-NEXT:    vpsllw $15, %xmm1, %xmm1
+; AVX512BW-NEXT:    vpmovw2m %xmm1, %k1
+; AVX512BW-NEXT:    vmovdqa32 %ymm0, 0 {%k1}
+; AVX512BW-NEXT:    vpxor %xmm1, %xmm1, %xmm1
+; AVX512BW-NEXT:    vpxor %xmm0, %xmm0, %xmm0
+; AVX512BW-NEXT:    kxorq %k0, %k0, %k1
+; AVX512BW-NEXT:    vzeroupper
+; AVX512BW-NEXT:    retq
+  tail call void @llvm.masked.store.v8i32.p0(<8 x i32> %arg, ptr null, i32 32, <8 x i1> %mask)
+  ret void
+}
+
+attributes #0 = { "zero-call-used-regs"="used" }

RKSimon

LGTM - @phoebewang ?

phoebewang

LGTM, too.

…r` (llvm#163358) In `buildClearRegister` use the correct pseudo-opcode for each register class: - For `VR128`, use `V_SET0` - For `VR256`, use `AVX_SET0` - For `VR512`, use `AVX512_512_SET0` - For `VK*`, use `KSET0Q/KSET0W` This avoids illegal register/opcode pairings and machine verifier errors when clearing call-used registers under `-fzero-call-used-regs=used`. Fixes: llvm#163053 --------- Co-authored-by: Simon Pilgrim <llvm-dev@redking.me.uk> (cherry picked from commit 228dae7)

github-actions · 2025-10-27T10:02:58Z

@RKSimon (or anyone else). If you would like to add a note about this fix in the release notes (completely optional). Please reply to this comment with a one or two sentence description of the fix. When you are done, please add the release:note label to this PR.

llvmbot added this to the LLVM 21.x Release milestone Oct 18, 2025

github-project-automation bot added this to LLVM Release Status Oct 18, 2025

github-project-automation bot moved this to Needs Triage in LLVM Release Status Oct 18, 2025

llvmbot requested a review from RKSimon October 18, 2025 11:46

llvmbot added the backend:X86 label Oct 18, 2025

llvmbot mentioned this pull request Oct 18, 2025

[clang] Miscompiles OpenSSH 10.x's mlkem768 key-exchange protocol when avx512 is enabled. #163053

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RKSimon requested a review from phoebewang October 18, 2025 11:48

c-rhodes moved this from Needs Triage to Needs Review in LLVM Release Status Oct 20, 2025

RKSimon approved these changes Oct 21, 2025

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phoebewang approved these changes Oct 21, 2025

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c-rhodes moved this from Needs Review to Needs Merge in LLVM Release Status Oct 22, 2025

c-rhodes force-pushed the issue163053 branch from 8ec2f6d to 2cdfa9d Compare October 27, 2025 10:02

c-rhodes merged commit 2cdfa9d into llvm:release/21.x Oct 27, 2025
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github-project-automation bot moved this from Needs Merge to Done in LLVM Release Status Oct 27, 2025

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release/21.x: [X86] Use pseudo instructions to zero registers in `buildClearRegister` (#163358) #164076

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release/21.x: [X86] Use pseudo instructions to zero registers in `buildClearRegister` (#163358) #164076

release/21.x: [X86] Use pseudo instructions to zero registers in `buildClearRegister` (#163358) #164076