[InstCombine] Allow Ephemerals when trying to remove assume.

[andjo403]

Makes it possible to remove loads of nonnull pointers when the only use is an assume.

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: Andreas Jonson (andjo403)

Changes

Makes it possible to remove loads of nonnull pointers when the only use is an assume.

---

Full diff: https://github.com/llvm/llvm-project/pull/128296.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp (+2-1)
• (modified) llvm/test/Transforms/InstCombine/assume.ll (+5-14)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
index 54f777ab20a7a..405b0c2d8d972 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCalls.cpp
@@ -3217,7 +3217,8 @@ Instruction *InstCombinerImpl::visitCallInst(CallInst &CI) {
                                         m_Zero())) &&
         LHS->getOpcode() == Instruction::Load &&
         LHS->getType()->isPointerTy() &&
-        isValidAssumeForContext(II, LHS, &DT)) {
+        isValidAssumeForContext(II, LHS, &DT,
+                                /*AllowEphemerals=*/true)) {
       MDNode *MD = MDNode::get(II->getContext(), {});
       LHS->setMetadata(LLVMContext::MD_nonnull, MD);
       LHS->setMetadata(LLVMContext::MD_noundef, MD);
diff --git a/llvm/test/Transforms/InstCombine/assume.ll b/llvm/test/Transforms/InstCombine/assume.ll
index 90fa9e680bb1e..5bd8fbc823756 100644
--- a/llvm/test/Transforms/InstCombine/assume.ll
+++ b/llvm/test/Transforms/InstCombine/assume.ll
@@ -502,10 +502,9 @@ define i1 @nonnull3B(ptr %a, i1 %control) {
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    br i1 [[CONTROL:%.*]], label [[TAKEN:%.*]], label [[NOT_TAKEN:%.*]]
 ; CHECK:       taken:
-; CHECK-NEXT:    [[LOAD:%.*]] = load ptr, ptr [[A:%.*]], align 8
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne ptr [[LOAD]], null
-; CHECK-NEXT:    call void @llvm.assume(i1 [[CMP]]) [ "nonnull"(ptr [[LOAD]]) ]
-; CHECK-NEXT:    ret i1 [[CMP]]
+; CHECK-NEXT:    [[LOAD:%.*]] = load ptr, ptr [[A:%.*]], align 8, !nonnull [[META6]], !noundef [[META6]]
+; CHECK-NEXT:    call void @llvm.assume(i1 true) [ "nonnull"(ptr [[LOAD]]) ]
+; CHECK-NEXT:    ret i1 true
 ; CHECK:       not_taken:
 ; CHECK-NEXT:    ret i1 false
 ;
@@ -582,16 +581,8 @@ not_taken:
 }
 
 define void @nonnull_only_ephemeral_use(ptr %p) {
-; DEFAULT-LABEL: @nonnull_only_ephemeral_use(
-; DEFAULT-NEXT:    [[A:%.*]] = load ptr, ptr [[P:%.*]], align 8
-; DEFAULT-NEXT:    [[CMP:%.*]] = icmp ne ptr [[A]], null
-; DEFAULT-NEXT:    tail call void @llvm.assume(i1 [[CMP]])
-; DEFAULT-NEXT:    ret void
-;
-; BUNDLES-LABEL: @nonnull_only_ephemeral_use(
-; BUNDLES-NEXT:    [[A:%.*]] = load ptr, ptr [[P:%.*]], align 8
-; BUNDLES-NEXT:    call void @llvm.assume(i1 true) [ "nonnull"(ptr [[A]]) ]
-; BUNDLES-NEXT:    ret void
+; CHECK-LABEL: @nonnull_only_ephemeral_use(
+; CHECK-NEXT:    ret void
 ;
   %a = load ptr, ptr %p
   %cmp = icmp ne ptr %a, null

[andjo403]

hmm is it strange to remove the condition in the assume in this fold as it can result in that all the information about the assume is removed if the load is not needed.

[andjo403]

from what I found here dtcxzyw/llvm-opt-benchmark#2154 (comment) I do not think that this the the way to go.