[DSE] Relax constraint on isGuaranteedLoopInvariant

If the location ptr to be killed is in no loop and the Function does not have irreducible loops, then we can regard it as loop invariant. Differential Revision: https://reviews.llvm.org/D135369
llvm · Oct 6, 2022 · eaf6e2f · eaf6e2f
1 parent 7329dc0
commit eaf6e2f
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Showing 3 changed files with 30 additions and 4 deletions.
diff --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -1215,8 +1215,10 @@ struct DSEState {
       if (GEP->hasAllConstantIndices())
         Ptr = GEP->getPointerOperand()->stripPointerCasts();
 
-    if (auto *I = dyn_cast<Instruction>(Ptr))
-      return I->getParent()->isEntryBlock();
+    if (auto *I = dyn_cast<Instruction>(Ptr)) {
+      return I->getParent()->isEntryBlock() ||
+             (!ContainsIrreducibleLoops && !LI.getLoopFor(I->getParent()));
+    }
     return true;
   }
 

diff --git a/llvm/test/Transforms/DeadStoreElimination/multiblock-loops.ll b/llvm/test/Transforms/DeadStoreElimination/multiblock-loops.ll
@@ -617,6 +617,32 @@ exit:
   ret i16 0
 }
 
+define i16 @irreducible_entryblock_def(i1 %c) {
+; CHECK-LABEL: @irreducible_entryblock_def(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[C:%.*]], label [[A:%.*]], label [[B:%.*]]
+; CHECK:       A:
+; CHECK-NEXT:    br label [[B]]
+; CHECK:       B:
+; CHECK-NEXT:    br i1 [[C]], label [[EXIT:%.*]], label [[A]]
+; CHECK:       exit:
+; CHECK-NEXT:    ret i16 0
+;
+entry:
+  %obj = alloca i32, align 4
+  br i1 %c, label %A, label %B
+
+A:
+  store i32 1, ptr %obj, align 4
+  br label %B
+
+B:
+  br i1 %c, label %exit, label %A
+
+exit:
+  ret i16 0
+}
+
 ; An irreducible loop inside another loop.
 define i16 @irreducible_nested() {
 ; CHECK-LABEL: @irreducible_nested(
@@ -846,7 +872,6 @@ define i16 @partial_override_overloop(i1 %c, i32 %i) {
 ; CHECK-NEXT:    br label [[FIRST:%.*]]
 ; CHECK:       first:
 ; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds [10 x i16], ptr @x, i16 0, i32 [[I:%.*]]
-; CHECK-NEXT:    store i16 1, ptr [[ARRAYIDX]], align 1
 ; CHECK-NEXT:    br label [[DO_BODY:%.*]]
 ; CHECK:       do.body:
 ; CHECK-NEXT:    [[I_0:%.*]] = phi i16 [ 0, [[FIRST]] ], [ [[INC:%.*]], [[DO_BODY]] ]

diff --git a/llvm/test/Transforms/DeadStoreElimination/multiblock-malloc-free.ll b/llvm/test/Transforms/DeadStoreElimination/multiblock-malloc-free.ll
@@ -170,7 +170,6 @@ define void @test27() {
 ; CHECK-NEXT:    br i1 true, label [[BB2:%.*]], label [[BB3:%.*]]
 ; CHECK:       bb2:
 ; CHECK-NEXT:    [[M:%.*]] = call noalias ptr @malloc(i64 10)
-; CHECK-NEXT:    store i8 1, ptr [[M]], align 1
 ; CHECK-NEXT:    br label [[BB3]]
 ; CHECK:       bb3:
 ; CHECK-NEXT:    [[R:%.*]] = phi ptr [ null, [[BB1:%.*]] ], [ [[M]], [[BB2]] ]