[llvm] [InstCombine] Fold `mul (sext bool X), Y` into `select X, -Y, 0` (PR #84792)

[Yingwei Zheng via llvm-commits]

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@@ -448,6 +448,20 @@ Instruction *InstCombinerImpl::visitMul(BinaryOperator &I) {
   if (match(Op1, m_ZExt(m_Value(X))) && X->getType()->isIntOrIntVectorTy(1))
     return SelectInst::Create(X, Op0, ConstantInt::getNullValue(Ty));
 
+  // mul (sext X), Y -> select X, -Y, 0
+  // mul Y, (sext X) -> select X, -Y, 0
+  Value *SExtOp;
+  if (match(Op0, m_OneUse(m_SExt(m_Value(SExtOp)))) &&
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dtcxzyw wrote:

Please add the following tests: https://godbolt.org/z/9856M5M8d
```
define i32 @test_mul_sext_bool(i1 %x, i32 %y) {
  %sext = sext i1 %x to i32
  %mul = mul i32 %sext, %y
  ret i32 %mul
}

define i32 @test_mul_sext_bool_nuw(i1 %x, i32 %y) {
  %sext = sext i1 %x to i32
  %mul = mul nuw i32 %sext, %y
  ret i32 %mul
}

define i32 @test_mul_sext_bool_nsw(i1 %x, i32 %y) {
  %sext = sext i1 %x to i32
  %mul = mul nsw i32 %sext, %y
  ret i32 %mul
}

define i32 @test_mul_sext_bool_nuw_nsw(i1 %x, i32 %y) {
  %sext = sext i1 %x to i32
  %mul = mul nuw nsw i32 %sext, %y
  ret i32 %mul
}

define i32 @test_mul_sext_bool_commuted(i1 %x, i32 %y) {
  %yy = xor i32 %y, 1 ; thwart complexity-based canonicalization
  %sext = sext i1 %x to i32
  %mul = mul i32 %yy, %sext
  ret i32 %mul
}

define i32 @test_mul_sext_nonbool(i2 %x, i32 %y) {
  %sext = sext i2 %x to i32
  %mul = mul i32 %sext, %y
  ret i32 %mul
}

define i32 @test_mul_sext_multiuse(i1 %x, i32 %y) {
  %sext = sext i1 %x to i32
  call void @use(i32 %sext)
  %mul = mul i32 %sext, %y
  ret i32 %mul
}

declare void @use(i32 %x)
```

https://github.com/llvm/llvm-project/pull/84792