[llvm] [InstCombine] Relax the one-use constraints for `icmp pred (binop X, Z), (binop Y, Z)` (PR #76384)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Yingwei Zheng (dtcxzyw)

<details>
<summary>Changes</summary>

This patch relaxes the one-use constraints for `icmp pred (binop X, Z), (binop Y, Z)`. It will enable more optimizations with pointer arithmetic.
One example in `boost::match_results::set_size`:

```
declare void @<!-- -->use(i64)
define i1 @<!-- -->src(ptr %a1, ptr %a2, ptr %add.ptr.i66, i64 %sub.ptr.rhs.cast.i) {
  %sub.ptr.lhs.cast.i = ptrtoint ptr %a1 to i64
  %sub.ptr.rhs.cast.i = ptrtoint ptr %a2 to i64
  %sub.ptr.sub.i = sub i64 %sub.ptr.lhs.cast.i, %sub.ptr.rhs.cast.i
  %sub.ptr.div.i = sdiv exact i64 %sub.ptr.sub.i, 24
  call void @<!-- -->use(i64 %sub.ptr.div.i)
  %sub.ptr.lhs.cast.i.i = ptrtoint ptr %add.ptr.i66 to i64
  %sub.ptr.sub.i.i = sub i64 %sub.ptr.lhs.cast.i.i, %sub.ptr.rhs.cast.i
  %sub.ptr.div.i.i = sdiv exact i64 %sub.ptr.sub.i.i, 24
  %cmp.i.not.i.i = icmp eq i64 %sub.ptr.div.i.i, %sub.ptr.div.i
  ret i1 %cmp.i.not.i.i
}
define i1 @<!-- -->tgt(ptr %a1, ptr %a2, ptr %add.ptr.i66, i64 %sub.ptr.rhs.cast.i) {
  %sub.ptr.lhs.cast.i = ptrtoint ptr %a1 to i64
  %sub.ptr.rhs.cast.i = ptrtoint ptr %a2 to i64
  %sub.ptr.sub.i = sub i64 %sub.ptr.lhs.cast.i, %sub.ptr.rhs.cast.i
  %sub.ptr.div.i = sdiv exact i64 %sub.ptr.sub.i, 24
  call void @<!-- -->use(i64 %sub.ptr.div.i)
  %cmp.i.not.i.i = icmp eq i64 %sub.ptr.sub.i.i, %sub.ptr.sub.i
  ret i1 %cmp.i.not.i.i
}
```




---
Full diff: https://github.com/llvm/llvm-project/pull/76384.diff


2 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp (+2-2) 
- (modified) llvm/test/Transforms/InstCombine/icmp.ll (+17) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 289976718e52f3..0afb415a482411 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -4911,8 +4911,8 @@ Instruction *InstCombinerImpl::foldICmpBinOp(ICmpInst &I,
     }
   }
 
-  if (BO0 && BO1 && BO0->getOpcode() == BO1->getOpcode() && BO0->hasOneUse() &&
-      BO1->hasOneUse() && BO0->getOperand(1) == BO1->getOperand(1)) {
+  if (BO0 && BO1 && BO0->getOpcode() == BO1->getOpcode() &&
+      BO0->getOperand(1) == BO1->getOperand(1)) {
     switch (BO0->getOpcode()) {
     default:
       break;
diff --git a/llvm/test/Transforms/InstCombine/icmp.ll b/llvm/test/Transforms/InstCombine/icmp.ll
index 1c7bb36f0d34c0..6d881be56dc2b4 100644
--- a/llvm/test/Transforms/InstCombine/icmp.ll
+++ b/llvm/test/Transforms/InstCombine/icmp.ll
@@ -815,6 +815,23 @@ define i1 @test46(i32 %X, i32 %Y, i32 %Z) {
   ret i1 %C
 }
 
+define i1 @test46_multiuse(i32 %X, i32 %Y, i32 %Z) {
+; CHECK-LABEL: @test46_multiuse(
+; CHECK-NEXT:    [[A:%.*]] = ashr exact i32 [[X:%.*]], [[Z:%.*]]
+; CHECK-NEXT:    call void @use_i32(i32 [[A]])
+; CHECK-NEXT:    [[B:%.*]] = ashr exact i32 [[Y:%.*]], [[Z]]
+; CHECK-NEXT:    call void @use_i32(i32 [[B]])
+; CHECK-NEXT:    [[C:%.*]] = icmp ult i32 [[X]], [[Y]]
+; CHECK-NEXT:    ret i1 [[C]]
+;
+  %A = ashr exact i32 %X, %Z
+  call void @use_i32(i32 %A)
+  %B = ashr exact i32 %Y, %Z
+  call void @use_i32(i32 %B)
+  %C = icmp ult i32 %A, %B
+  ret i1 %C
+}
+
 ; PR9343 #5
 define i1 @test47(i32 %X, i32 %Y, i32 %Z) {
 ; CHECK-LABEL: @test47(

``````````

</details>


https://github.com/llvm/llvm-project/pull/76384