[llvm] 05ca9eb - [X86] Make `(shift X (xor/sub N-1, Y))` -> `(shift X, (not Y))` check for one use.

[Noah Goldstein via llvm-commits]

Author: Noah Goldstein
Date: 2023-02-28T23:25:16-06:00
New Revision: 05ca9ebc0433b4e19fc67c1dd023414bc6357f09

URL: https://github.com/llvm/llvm-project/commit/05ca9ebc0433b4e19fc67c1dd023414bc6357f09
DIFF: https://github.com/llvm/llvm-project/commit/05ca9ebc0433b4e19fc67c1dd023414bc6357f09.diff

LOG: [X86] Make `(shift X (xor/sub N-1, Y))` -> `(shift X, (not Y))` check for one use.

`(xor/sub N-1, Y)` -> `(not Y)` is minorly preferable (especially for
`(sub N-1, Y)` where it saves an instruction), but isn't worth
potentially creating an extra instruction for.

So, only do the transformation if `(xor/sub N-1, Y)` has one use.

Reviewed By: RKSimon

Differential Revision: https://reviews.llvm.org/D144985

Added: 
    

Modified: 
    llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
    llvm/test/CodeGen/X86/pr61038.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
index b45b6eed7764..c13245ff7bea 100644
--- a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -4007,7 +4007,7 @@ bool X86DAGToDAGISel::tryShiftAmountMod(SDNode *N) {
     if (Add1C && Add1C->getAPIntValue().urem(Size) == 0) {
       NewShiftAmt = Add0;
 
-    } else if (ShiftAmt->getOpcode() != ISD::ADD &&
+    } else if (ShiftAmt->getOpcode() != ISD::ADD && ShiftAmt.hasOneUse() &&
                ((Add0C && Add0C->getAPIntValue().urem(Size) == Size - 1) ||
                 (Add1C && Add1C->getAPIntValue().urem(Size) == Size - 1))) {
       // If we are doing a NOT on just the lower bits with (Size*N-1) -/^ X

diff  --git a/llvm/test/CodeGen/X86/pr61038.ll b/llvm/test/CodeGen/X86/pr61038.ll
index 2db78234b3be..82418cf5946a 100644
--- a/llvm/test/CodeGen/X86/pr61038.ll
+++ b/llvm/test/CodeGen/X86/pr61038.ll
@@ -9,28 +9,24 @@ define void @test_61038(ptr %tmp_buffer) {
 ; CHECK-BMI2:       # %bb.0: # %entry
 ; CHECK-BMI2-NEXT:    tzcntl %eax, %eax
 ; CHECK-BMI2-NEXT:    movabsq $8589934591, %rcx # imm = 0x1FFFFFFFF
-; CHECK-BMI2-NEXT:    movq $-1, %rdx
+; CHECK-BMI2-NEXT:    movq %rcx, %rdx
 ; CHECK-BMI2-NEXT:    btcq %rax, %rdx
-; CHECK-BMI2-NEXT:    shrxq %rdx, %rcx, %rdx
-; CHECK-BMI2-NEXT:    btcq %rax, %rcx
 ; CHECK-BMI2-NEXT:    xorl %eax, %eax
-; CHECK-BMI2-NEXT:    cmpq $64, %rcx
-; CHECK-BMI2-NEXT:    cmovael %eax, %edx
-; CHECK-BMI2-NEXT:    movl %edx, (%rdi)
+; CHECK-BMI2-NEXT:    cmpq $64, %rdx
+; CHECK-BMI2-NEXT:    shrxq %rdx, %rcx, %rcx
+; CHECK-BMI2-NEXT:    cmovael %eax, %ecx
+; CHECK-BMI2-NEXT:    movl %ecx, (%rdi)
 ; CHECK-BMI2-NEXT:    retq
 ;
 ; CHECK-BMI-LABEL: test_61038:
 ; CHECK-BMI:       # %bb.0: # %entry
 ; CHECK-BMI-NEXT:    tzcntl %eax, %eax
 ; CHECK-BMI-NEXT:    movabsq $8589934591, %rdx # imm = 0x1FFFFFFFF
-; CHECK-BMI-NEXT:    movq %rdx, %rsi
-; CHECK-BMI-NEXT:    btcq %rax, %rsi
-; CHECK-BMI-NEXT:    movq $-1, %rcx
+; CHECK-BMI-NEXT:    movq %rdx, %rcx
 ; CHECK-BMI-NEXT:    btcq %rax, %rcx
-; CHECK-BMI-NEXT:    # kill: def $cl killed $cl killed $rcx
 ; CHECK-BMI-NEXT:    shrq %cl, %rdx
 ; CHECK-BMI-NEXT:    xorl %eax, %eax
-; CHECK-BMI-NEXT:    cmpq $64, %rsi
+; CHECK-BMI-NEXT:    cmpq $64, %rcx
 ; CHECK-BMI-NEXT:    cmovael %eax, %edx
 ; CHECK-BMI-NEXT:    movl %edx, (%rdi)
 ; CHECK-BMI-NEXT:    retq