[DAGCombiner][X86][AArch64][SPARC][SystemZ] y - (x + C) -> (y - x) - …

…C fold. Try 2

Summary:
Direct sibling of D62223 patch.
While i don't have a direct motivational pattern for this,
it would seem to make sense to handle both patterns (or none),
for symmetry?

The aarch64 changes look neutral;
sparc and systemz look like improvement (one less instruction each);
x86 changes - 32bit case improves, 64bit case shows that LEA no longer
gets constructed, which may be because that whole test is `-mattr=+slow-lea,+slow-3ops-lea`

https://rise4fun.com/Alive/ffh

This is a recommit, originally committed in rL361853, but reverted
to investigate test-suite compile-time hangs.

Reviewers: RKSimon, craig.topper, spatel, t.p.northover

Reviewed By: t.p.northover

Subscribers: t.p.northover, jyknight, javed.absar, kristof.beyls, fedor.sergeev, jrtc27, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D62252

llvm-svn: 361872

llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp

@@ -2929,6 +2929,12 @@ SDValue DAGCombiner::visitSUB(SDNode *N) {
     SDValue Sub = DAG.getNode(ISD::SUB, DL, VT, N0.getOperand(0), N1);
     return DAG.getNode(ISD::ADD, DL, VT, Sub, N0.getOperand(1));
   }
+  // y - (x + C)  ->  (y - x) - C
+  if (N1.hasOneUse() && N1.getOpcode() == ISD::ADD &&
+      isConstantOrConstantVector(N1.getOperand(1))) {
+    SDValue Sub = DAG.getNode(ISD::SUB, DL, VT, N0, N1.getOperand(0));
+    return DAG.getNode(ISD::SUB, DL, VT, Sub, N1.getOperand(1));
+  }
 
   // If the target's bool is represented as 0/-1, prefer to make this 'add 0/-1'
   // rather than 'sub 0/1' (the sext should get folded).

llvm/test/CodeGen/AArch64/shift-amount-mod.ll

@@ -513,7 +513,7 @@ define i64 @reg64_lshr_by_negated_unfolded_sub_b(i64 %val, i64 %a, i64 %b) nounw
 define i32 @reg32_lshr_by_b_sub_negated_unfolded(i32 %val, i32 %a, i32 %b) nounwind {
 ; CHECK-LABEL: reg32_lshr_by_b_sub_negated_unfolded:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    add w8, w1, w2
+; CHECK-NEXT:    add w8, w2, w1
 ; CHECK-NEXT:    lsr w0, w0, w8
 ; CHECK-NEXT:    ret
   %nega = sub i32 0, %a
@@ -525,7 +525,7 @@ define i32 @reg32_lshr_by_b_sub_negated_unfolded(i32 %val, i32 %a, i32 %b) nounw
 define i64 @reg64_lshr_by_b_sub_negated_unfolded(i64 %val, i64 %a, i64 %b) nounwind {
 ; CHECK-LABEL: reg64_lshr_by_b_sub_negated_unfolded:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    add x8, x1, x2
+; CHECK-NEXT:    add x8, x2, x1
 ; CHECK-NEXT:    lsr x0, x0, x8
 ; CHECK-NEXT:    ret
   %nega = sub i64 0, %a

llvm/test/CodeGen/AArch64/sink-addsub-of-const.ll

@@ -107,9 +107,9 @@ define i32 @sink_add_of_const_to_sub(i32 %a, i32 %b, i32 %c) {
 define i32 @sink_add_of_const_to_sub2(i32 %a, i32 %b, i32 %c) {
 ; CHECK-LABEL: sink_add_of_const_to_sub2:
 ; CHECK:       // %bb.0:
-; CHECK-NEXT:    sub w8, w0, w1
-; CHECK-NEXT:    add w8, w8, #32 // =32
-; CHECK-NEXT:    sub w0, w2, w8
+; CHECK-NEXT:    sub w8, w1, w0
+; CHECK-NEXT:    add w8, w2, w8
+; CHECK-NEXT:    sub w0, w8, #32 // =32
 ; CHECK-NEXT:    ret
   %t0 = sub i32 %a, %b
   %t1 = add i32 %t0, 32 ; constant always on RHS
@@ -295,9 +295,9 @@ define <4 x i32> @vec_sink_add_of_const_to_sub2(<4 x i32> %a, <4 x i32> %b, <4 x
 ; CHECK:       // %bb.0:
 ; CHECK-NEXT:    adrp x8, .LCPI19_0
 ; CHECK-NEXT:    ldr q3, [x8, :lo12:.LCPI19_0]
-; CHECK-NEXT:    sub v0.4s, v0.4s, v1.4s
-; CHECK-NEXT:    add v0.4s, v0.4s, v3.4s
-; CHECK-NEXT:    sub v0.4s, v2.4s, v0.4s
+; CHECK-NEXT:    sub v0.4s, v1.4s, v0.4s
+; CHECK-NEXT:    add v0.4s, v2.4s, v0.4s
+; CHECK-NEXT:    sub v0.4s, v0.4s, v3.4s
 ; CHECK-NEXT:    ret
   %t0 = sub <4 x i32> %a, %b
   %t1 = add <4 x i32> %t0, <i32 42, i32 24, i32 undef, i32 46> ; constant always on RHS

llvm/test/CodeGen/SPARC/2013-05-17-CallFrame.ll

@@ -15,10 +15,9 @@ define void @variable_alloca_with_adj_call_stack(i32 %num) {
 ; V8-NEXT:    .cfi_register 15, 31
 ; V8-NEXT:    add %i0, 7, %i0
 ; V8-NEXT:    and %i0, -8, %i0
-; V8-NEXT:    add %i0, 8, %i0
 ; V8-NEXT:    sub %sp, %i0, %i0
-; V8-NEXT:    add %i0, 96, %o0
-; V8-NEXT:    mov %i0, %sp
+; V8-NEXT:    add %i0, -8, %sp
+; V8-NEXT:    add %i0, 88, %o0
 ; V8-NEXT:    add %sp, -16, %sp
 ; V8-NEXT:    st %o0, [%sp+104]
 ; V8-NEXT:    st %o0, [%sp+100]

llvm/test/CodeGen/SystemZ/alloca-03.ll

@@ -75,13 +75,12 @@ define void @f3(i64 %len) {
 ; CHECK-NEXT:    lgr %r11, %r15
 ; CHECK-NEXT:    .cfi_def_cfa_register %r11
 ; CHECK-NEXT:    lgr %r1, %r15
-; CHECK-NEXT:    sllg %r2, %r2, 3
-; CHECK-NEXT:    la %r0, 120(%r2)
+; CHECK-NEXT:    sllg %r0, %r2, 3
 ; CHECK-NEXT:    sgr %r1, %r0
-; CHECK-NEXT:    la %r2, 280(%r1)
-; CHECK-NEXT:    nill %r2, 65408
-; CHECK-NEXT:    lgr %r15, %r1
-; CHECK-NEXT:    mvghi 0(%r2), 10
+; CHECK-NEXT:    lay %r15, -120(%r1)
+; CHECK-NEXT:    la %r1, 160(%r1)
+; CHECK-NEXT:    nill %r1, 65408
+; CHECK-NEXT:    mvghi 0(%r1), 10
 ; CHECK-NEXT:    lmg %r11, %r15, 248(%r11)
 ; CHECK-NEXT:    br %r14
   %x = alloca i64, i64 %len, align 128

llvm/test/CodeGen/X86/sink-addsub-of-const.ll

@@ -178,16 +178,16 @@ define i32 @sink_add_of_const_to_sub2(i32 %a, i32 %b, i32 %c) {
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %eax
 ; X32-NEXT:    movl {{[0-9]+}}(%esp), %ecx
 ; X32-NEXT:    subl {{[0-9]+}}(%esp), %ecx
-; X32-NEXT:    addl $32, %ecx
-; X32-NEXT:    subl %ecx, %eax
+; X32-NEXT:    addl %ecx, %eax
+; X32-NEXT:    addl $-32, %eax
 ; X32-NEXT:    retl
 ;
 ; X64-LABEL: sink_add_of_const_to_sub2:
 ; X64:       # %bb.0:
-; X64-NEXT:    movl %edx, %eax
-; X64-NEXT:    subl %esi, %edi
-; X64-NEXT:    addl $32, %edi
-; X64-NEXT:    subl %edi, %eax
+; X64-NEXT:    # kill: def $edx killed $edx def $rdx
+; X64-NEXT:    # kill: def $esi killed $esi def $rsi
+; X64-NEXT:    subl %edi, %esi
+; X64-NEXT:    leal -32(%rdx,%rsi), %eax
 ; X64-NEXT:    retq
   %t0 = sub i32 %a, %b
   %t1 = add i32 %t0, 32 ; constant always on RHS
@@ -434,18 +434,18 @@ define <4 x i32> @vec_sink_add_of_const_to_sub(<4 x i32> %a, <4 x i32> %b, <4 x
 define <4 x i32> @vec_sink_add_of_const_to_sub2(<4 x i32> %a, <4 x i32> %b, <4 x i32> %c) {
 ; X32-LABEL: vec_sink_add_of_const_to_sub2:
 ; X32:       # %bb.0:
-; X32-NEXT:    psubd %xmm1, %xmm0
-; X32-NEXT:    paddd {{\.LCPI.*}}, %xmm0
-; X32-NEXT:    psubd %xmm0, %xmm2
-; X32-NEXT:    movdqa %xmm2, %xmm0
+; X32-NEXT:    psubd %xmm0, %xmm1
+; X32-NEXT:    paddd %xmm2, %xmm1
+; X32-NEXT:    psubd {{\.LCPI.*}}, %xmm1
+; X32-NEXT:    movdqa %xmm1, %xmm0
 ; X32-NEXT:    retl
 ;
 ; X64-LABEL: vec_sink_add_of_const_to_sub2:
 ; X64:       # %bb.0:
-; X64-NEXT:    psubd %xmm1, %xmm0
-; X64-NEXT:    paddd {{.*}}(%rip), %xmm0
-; X64-NEXT:    psubd %xmm0, %xmm2
-; X64-NEXT:    movdqa %xmm2, %xmm0
+; X64-NEXT:    psubd %xmm0, %xmm1
+; X64-NEXT:    paddd %xmm2, %xmm1
+; X64-NEXT:    psubd {{.*}}(%rip), %xmm1
+; X64-NEXT:    movdqa %xmm1, %xmm0
 ; X64-NEXT:    retq
   %t0 = sub <4 x i32> %a, %b
   %t1 = add <4 x i32> %t0, <i32 42, i32 24, i32 undef, i32 46> ; constant always on RHS