[InstCombine] Handle commuted pattern for ((X s/ C1) << C2) + X

[dtcxzyw]

Closes #121700

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

Changes

Closes #121700

---

Full diff: https://github.com/llvm/llvm-project/pull/121737.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp (+4-3)
• (modified) llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll (+11)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
index 7a184a19d7c54a..74d17067de16e5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineAddSub.cpp
@@ -1625,12 +1625,13 @@ Instruction *InstCombinerImpl::visitAdd(BinaryOperator &I) {
 
   // ((X s/ C1) << C2) + X => X s% -C1 where -C1 is 1 << C2
   const APInt *C1, *C2;
-  if (match(LHS, m_Shl(m_SDiv(m_Specific(RHS), m_APInt(C1)), m_APInt(C2)))) {
+  if (match(&I, m_c_Add(m_Shl(m_SDiv(m_Value(A), m_APInt(C1)), m_APInt(C2)),
+                        m_Deferred(A)))) {
     APInt one(C2->getBitWidth(), 1);
     APInt minusC1 = -(*C1);
     if (minusC1 == (one << *C2)) {
-      Constant *NewRHS = ConstantInt::get(RHS->getType(), minusC1);
-      return BinaryOperator::CreateSRem(RHS, NewRHS);
+      Constant *NewRHS = ConstantInt::get(A->getType(), minusC1);
+      return BinaryOperator::CreateSRem(A, NewRHS);
     }
   }
 
diff --git a/llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll b/llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll
index 84462f9a7f592b..d4edf12eba6acf 100644
--- a/llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll
+++ b/llvm/test/Transforms/InstCombine/add-shl-sdiv-to-srem.ll
@@ -12,6 +12,17 @@ define i8 @add-shl-sdiv-scalar0(i8 %x) {
   ret i8 %rz
 }
 
+define i8 @add-shl-sdiv-scalar0_commuted(i8 %x) {
+; CHECK-LABEL: @add-shl-sdiv-scalar0_commuted(
+; CHECK-NEXT:    [[RZ:%.*]] = srem i8 [[X:%.*]], 4
+; CHECK-NEXT:    ret i8 [[RZ]]
+;
+  %sd = sdiv i8 %x, -4
+  %sl = shl i8 %sd, 2
+  %rz = add i8 %x, %sl
+  ret i8 %rz
+}
+
 define i8 @add-shl-sdiv-scalar1(i8 %x) {
 ; CHECK-LABEL: @add-shl-sdiv-scalar1(
 ; CHECK-NEXT:    [[RZ:%.*]] = srem i8 [[X:%.*]], 64

[nikic]

LGTM. An alternative would be to move this to foldAddLikeCommutative.