From 05ca9ebc0433b4e19fc67c1dd023414bc6357f09 Mon Sep 17 00:00:00 2001
From: Noah Goldstein <goldstein.w.n@gmail.com>
Date: Tue, 28 Feb 2023 22:21:53 -0600
Subject: [PATCH] [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
---
 llvm/lib/Target/X86/X86ISelDAGToDAG.cpp |  2 +-
 llvm/test/CodeGen/X86/pr61038.ll        | 18 +++++++-----------
 2 files changed, 8 insertions(+), 12 deletions(-)

diff --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
index b45b6ee..c13245f 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 2db7823..82418cf 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
-- 
2.7.4