[llvm] [InstCombine] Resolve TODO: Remove one-time check if other logic operand (Y) is constant (PR #77973)

[via llvm-commits]

https://github.com/AtariDreams updated https://github.com/llvm/llvm-project/pull/77973

>From a6591537764e5fd0411f42617b9e6722ed87aa24 Mon Sep 17 00:00:00 2001
From: Rose <83477269+AtariDreams at users.noreply.github.com>
Date: Sun, 14 Jan 2024 12:53:37 -0500
Subject: [PATCH 1/2] [InstCombine] Add pre-commit tests [NFC]

---
 llvm/test/Transforms/InstCombine/shift-logic.ll | 15 +++++++++++++++
 1 file changed, 15 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/shift-logic.ll b/llvm/test/Transforms/InstCombine/shift-logic.ll
index 544694d398431e3..b2e047edd89938f 100644
--- a/llvm/test/Transforms/InstCombine/shift-logic.ll
+++ b/llvm/test/Transforms/InstCombine/shift-logic.ll
@@ -430,6 +430,21 @@ define i8 @shl_sub(i8 %x, i8 %y) {
   ret i8 %sh1
 }
 
+define i8 @shl_sub_multiuse(i8 %x) {
+; CHECK-LABEL: @shl_sub_multiuse(
+; CHECK-NEXT:    [[SH0:%.*]] = shl i8 [[X:%.*]], 3
+; CHECK-NEXT:    [[R:%.*]] = sub i8 [[SH0]], 42
+; CHECK-NEXT:    call void @use(i8 [[SH0]])
+; CHECK-NEXT:    [[SH1:%.*]] = shl i8 [[R]], 2
+; CHECK-NEXT:    ret i8 [[SH1]]
+;
+  %sh0 = shl i8 %x, 3
+  %r = sub i8 %sh0, 42
+  call void @use(i8 %sh0)
+  %sh1 = shl i8 %r, 2
+  ret i8 %sh1
+}
+
 ; Make sure we don't commute operands for sub
 define i8 @shl_sub_no_commute(i8 %x, i8 %y) {
 ; CHECK-LABEL: @shl_sub_no_commute(

>From 20b8d9b58ea03e7b38a8e24880876cc23e252cc3 Mon Sep 17 00:00:00 2001
From: Rose <83477269+AtariDreams at users.noreply.github.com>
Date: Fri, 12 Jan 2024 15:15:27 -0500
Subject: [PATCH 2/2] [Transforms] Remove one-time check if other logic operand
 (Y) is constant

By using match(W, m_ImmConstant()), we do not need to worry about one-time use anymore.
---
 llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp | 11 +++++------
 llvm/test/Transforms/InstCombine/shift-logic.ll       |  4 ++--
 2 files changed, 7 insertions(+), 8 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index b7958978c450c98..cbad2d6f8be7898 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -368,12 +368,11 @@ static Instruction *foldShiftOfShiftedBinOp(BinaryOperator &I,
 
   // Find a matching one-use shift by constant. The fold is not valid if the sum
   // of the shift values equals or exceeds bitwidth.
-  // TODO: Remove the one-use check if the other logic operand (Y) is constant.
   Value *X, *Y;
-  auto matchFirstShift = [&](Value *V) {
+  auto matchFirstShift = [&](Value *V, Value *W) {
     APInt Threshold(Ty->getScalarSizeInBits(), Ty->getScalarSizeInBits());
-    return match(V,
-                 m_OneUse(m_BinOp(ShiftOpcode, m_Value(X), m_Constant(C0)))) &&
+    return match(V, m_BinOp(ShiftOpcode, m_Value(X), m_Constant(C0))) &&
+           (V->hasOneUse() || match(W, m_ImmConstant())) &&
            match(ConstantExpr::getAdd(C0, C1),
                  m_SpecificInt_ICMP(ICmpInst::ICMP_ULT, Threshold));
   };
@@ -382,9 +381,9 @@ static Instruction *foldShiftOfShiftedBinOp(BinaryOperator &I,
   // is not so we cannot reoder if we match operand(1) and need to keep the
   // operands in their original positions.
   bool FirstShiftIsOp1 = false;
-  if (matchFirstShift(BinInst->getOperand(0)))
+  if (matchFirstShift(BinInst->getOperand(0), BinInst->getOperand(1)))
     Y = BinInst->getOperand(1);
-  else if (matchFirstShift(BinInst->getOperand(1))) {
+  else if (matchFirstShift(BinInst->getOperand(1), BinInst->getOperand(0))) {
     Y = BinInst->getOperand(0);
     FirstShiftIsOp1 = BinInst->getOpcode() == Instruction::Sub;
   } else
diff --git a/llvm/test/Transforms/InstCombine/shift-logic.ll b/llvm/test/Transforms/InstCombine/shift-logic.ll
index b2e047edd89938f..a96333a769fe1e0 100644
--- a/llvm/test/Transforms/InstCombine/shift-logic.ll
+++ b/llvm/test/Transforms/InstCombine/shift-logic.ll
@@ -433,9 +433,9 @@ define i8 @shl_sub(i8 %x, i8 %y) {
 define i8 @shl_sub_multiuse(i8 %x) {
 ; CHECK-LABEL: @shl_sub_multiuse(
 ; CHECK-NEXT:    [[SH0:%.*]] = shl i8 [[X:%.*]], 3
-; CHECK-NEXT:    [[R:%.*]] = sub i8 [[SH0]], 42
 ; CHECK-NEXT:    call void @use(i8 [[SH0]])
-; CHECK-NEXT:    [[SH1:%.*]] = shl i8 [[R]], 2
+; CHECK-NEXT:    [[R:%.*]] = shl i8 [[X]], 5
+; CHECK-NEXT:    [[SH1:%.*]] = add i8 [[R]], 88
 ; CHECK-NEXT:    ret i8 [[SH1]]
 ;
   %sh0 = shl i8 %x, 3