[llvm] [Reassociate] Drop weight reduction to fix issue 91417 (PR #91469)

[Yingwei Zheng via llvm-commits]

================
@@ -1,69 +1,100 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
 ; RUN: opt < %s -passes=reassociate -S | FileCheck %s
 
 ; Tests involving repeated operations on the same value.
 
 define i8 @nilpotent(i8 %x) {
-; CHECK-LABEL: @nilpotent(
+; CHECK-LABEL: define i8 @nilpotent(
+; CHECK-SAME: i8 [[X:%.*]]) {
+; CHECK-NEXT:    ret i8 0
+;
   %tmp = xor i8 %x, %x
   ret i8 %tmp
-; CHECK: ret i8 0
 }
 
 define i2 @idempotent(i2 %x) {
-; CHECK-LABEL: @idempotent(
+; CHECK-LABEL: define i2 @idempotent(
+; CHECK-SAME: i2 [[X:%.*]]) {
+; CHECK-NEXT:    ret i2 -1
----------------
dtcxzyw wrote:

@nikic Do you think this fix works? It will break iff there are more than 2^32 instructions in the IR. Anyway, I don't think it makes sense to choose i8 as type of the repeat count for fmul with fp8.

```
diff --git a/llvm/lib/Transforms/Scalar/Reassociate.cpp b/llvm/lib/Transforms/Scalar/Reassociate.cpp
index 04c54ed69e93..6e547b558316 100644
--- a/llvm/lib/Transforms/Scalar/Reassociate.cpp
+++ b/llvm/lib/Transforms/Scalar/Reassociate.cpp
@@ -384,8 +384,8 @@ static bool LinearizeExprTree(Instruction *I,
   assert((isa<UnaryOperator>(I) || isa<BinaryOperator>(I)) &&
          "Expected a UnaryOperator or BinaryOperator!");
   LLVM_DEBUG(dbgs() << "LINEARIZE: " << *I << '\n');
-  unsigned Bitwidth = I->getType()->getScalarType()->getPrimitiveSizeInBits();
   unsigned Opcode = I->getOpcode();
+  unsigned Bitwidth = (Instruction::isIdempotent(Opcode) || Opcode == Instruction::Mul || Opcode == Instruction::FMul) ? 32 : I->getType()->getScalarSizeInBits();
   assert(I->isAssociative() && I->isCommutative() &&
          "Expected an associative and commutative operation!");
 
diff --git a/llvm/test/Transforms/Reassociate/reassoc_bool_vec.ll b/llvm/test/Transforms/Reassociate/reassoc_bool_vec.ll
index bd0060cc5abb..d4aa5c507ec8 100644
--- a/llvm/test/Transforms/Reassociate/reassoc_bool_vec.ll
+++ b/llvm/test/Transforms/Reassociate/reassoc_bool_vec.ll
@@ -56,19 +56,20 @@ define <8 x i1> @vector2(<8 x i1> %a, <8 x i1> %b0, <8 x i1> %b1, <8 x i1> %b2,
 ; CHECK-NEXT:    [[OR5:%.*]] = or <8 x i1> [[B5]], [[A]]
 ; CHECK-NEXT:    [[OR6:%.*]] = or <8 x i1> [[B6]], [[A]]
 ; CHECK-NEXT:    [[OR7:%.*]] = or <8 x i1> [[B7]], [[A]]
-; CHECK-NEXT:    [[XOR0:%.*]] = xor <8 x i1> [[OR1]], [[OR0]]
-; CHECK-NEXT:    [[XOR2:%.*]] = xor <8 x i1> [[XOR0]], [[OR2]]
-; CHECK-NEXT:    [[OR045:%.*]] = xor <8 x i1> [[XOR2]], [[OR3]]
-; CHECK-NEXT:    [[XOR3:%.*]] = xor <8 x i1> [[OR045]], [[OR4]]
-; CHECK-NEXT:    [[XOR4:%.*]] = xor <8 x i1> [[XOR3]], [[OR5]]
-; CHECK-NEXT:    [[XOR5:%.*]] = xor <8 x i1> [[XOR4]], [[OR6]]
-; CHECK-NEXT:    [[XOR6:%.*]] = xor <8 x i1> [[XOR5]], [[OR7]]
+; CHECK-NEXT:    [[XOR2:%.*]] = xor <8 x i1> [[OR1]], [[OR0]]
+; CHECK-NEXT:    [[OR045:%.*]] = xor <8 x i1> [[XOR2]], [[OR2]]
+; CHECK-NEXT:    [[XOR3:%.*]] = xor <8 x i1> [[OR045]], [[OR3]]
+; CHECK-NEXT:    [[XOR4:%.*]] = xor <8 x i1> [[XOR3]], [[OR4]]
+; CHECK-NEXT:    [[XOR5:%.*]] = xor <8 x i1> [[XOR4]], [[OR5]]
+; CHECK-NEXT:    [[XOR6:%.*]] = xor <8 x i1> [[XOR5]], [[OR6]]
+; CHECK-NEXT:    [[XOR7:%.*]] = xor <8 x i1> [[XOR6]], [[OR7]]
 ; CHECK-NEXT:    [[OR4560:%.*]] = or <8 x i1> [[OR045]], [[XOR2]]
 ; CHECK-NEXT:    [[OR023:%.*]] = or <8 x i1> [[OR4560]], [[XOR3]]
 ; CHECK-NEXT:    [[OR001:%.*]] = or <8 x i1> [[OR023]], [[XOR4]]
 ; CHECK-NEXT:    [[OR0123:%.*]] = or <8 x i1> [[OR001]], [[XOR5]]
 ; CHECK-NEXT:    [[OR01234567:%.*]] = or <8 x i1> [[OR0123]], [[XOR6]]
-; CHECK-NEXT:    ret <8 x i1> [[OR01234567]]
+; CHECK-NEXT:    [[OR1234567:%.*]] = or <8 x i1> [[OR01234567]], [[XOR7]]
+; CHECK-NEXT:    ret <8 x i1> [[OR1234567]]
 ;
   %or0 = or <8 x i1> %b0, %a
   %or1 = or <8 x i1> %b1, %a
diff --git a/llvm/test/Transforms/Reassociate/repeats.ll b/llvm/test/Transforms/Reassociate/repeats.ll
index 28177f1c0ba5..7aa2b8a43213 100644
--- a/llvm/test/Transforms/Reassociate/repeats.ll
+++ b/llvm/test/Transforms/Reassociate/repeats.ll
@@ -15,7 +15,7 @@ define i8 @nilpotent(i8 %x) {
 define i2 @idempotent(i2 %x) {
 ; CHECK-LABEL: define i2 @idempotent(
 ; CHECK-SAME: i2 [[X:%.*]]) {
-; CHECK-NEXT:    ret i2 -1
+; CHECK-NEXT:    ret i2 [[X]]
 ;
   %tmp1 = and i2 %x, %x
   %tmp2 = and i2 %tmp1, %x
```

https://github.com/llvm/llvm-project/pull/91469