[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 c2d21f339a09bcf5d26016023a183774baccec50 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]

---
 .../Transforms/InstCombine/shift-logic.ll     | 30 +++++++++++++++++++
 1 file changed, 30 insertions(+)

diff --git a/llvm/test/Transforms/InstCombine/shift-logic.ll b/llvm/test/Transforms/InstCombine/shift-logic.ll
index 544694d398431e3..6e4f6bd83395eef 100644
--- a/llvm/test/Transforms/InstCombine/shift-logic.ll
+++ b/llvm/test/Transforms/InstCombine/shift-logic.ll
@@ -346,6 +346,36 @@ define i8 @shl_add(i8 %x, i8 %y) {
   ret i8 %sh1
 }
 
+define i8 @shl_add_multiuse(i8 %x) {
+; CHECK-LABEL: @shl_add_multiuse(
+; CHECK-NEXT:    [[SH0:%.*]] = shl i8 [[X:%.*]], 3
+; CHECK-NEXT:    [[R:%.*]] = add 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 = add i8 %sh0, -42
+  call void @use(i8 %sh0)
+  %sh1 = shl i8 %r, 2
+  ret i8 %sh1
+}
+
+define i8 @shl_add_multiuse_nonconstant(i8 %x, i8 %y) {
+; CHECK-LABEL: @shl_add_multiuse_nonconstant(
+; CHECK-NEXT:    [[SH0:%.*]] = shl i8 [[X:%.*]], 3
+; CHECK-NEXT:    [[R:%.*]] = add i8 [[SH0]], [[Y:%.*]]
+; 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 = add i8 %sh0, %y
+  call void @use(i8 %sh0)
+  %sh1 = shl i8 %r, 2
+  ret i8 %sh1
+}
+
 define <2 x i8> @shl_add_nonuniform(<2 x i8> %x, <2 x i8> %y) {
 ; CHECK-LABEL: @shl_add_nonuniform(
 ; CHECK-NEXT:    [[TMP1:%.*]] = shl <2 x i8> [[X:%.*]], <i8 5, i8 4>

>From 9fdbd5acf84d85a190c6254eb2375f3000b3689e 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.
---
 .../Transforms/InstCombine/InstCombineShifts.cpp | 16 ++++++++--------
 llvm/test/Transforms/InstCombine/shift-logic.ll  |  4 ++--
 2 files changed, 10 insertions(+), 10 deletions(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
index b7958978c450c98..54490c46dfaefcd 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -366,14 +366,14 @@ static Instruction *foldShiftOfShiftedBinOp(BinaryOperator &I,
 
   Type *Ty = I.getType();
 
-  // Find a matching one-use shift by constant. The fold is not valid if the sum
+  // Find a matching 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) {
-    APInt Threshold(Ty->getScalarSizeInBits(), Ty->getScalarSizeInBits());
-    return match(V,
-                 m_OneUse(m_BinOp(ShiftOpcode, m_Value(X), m_Constant(C0)))) &&
+  auto matchFirstShift = [&](Value *V, Value *W) {
+    unsigned Size = Ty->getScalarSizeInBits();
+    APInt Threshold(Size, Size);
+    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 +382,9 @@ 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 6e4f6bd83395eef..c982b45b504e9a1 100644
--- a/llvm/test/Transforms/InstCombine/shift-logic.ll
+++ b/llvm/test/Transforms/InstCombine/shift-logic.ll
@@ -349,9 +349,9 @@ define i8 @shl_add(i8 %x, i8 %y) {
 define i8 @shl_add_multiuse(i8 %x) {
 ; CHECK-LABEL: @shl_add_multiuse(
 ; CHECK-NEXT:    [[SH0:%.*]] = shl i8 [[X:%.*]], 3
-; CHECK-NEXT:    [[R:%.*]] = add 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