[llvm] e8723ab - [DSE] Check post-dominance for malloc+memset->calloc transform.

[Alina Sbirlea via llvm-commits]

Author: Alina Sbirlea
Date: 2021-08-23T12:39:51-07:00
New Revision: e8723abf43c37aff4d6d9b6ba131e345b74c7798

URL: https://github.com/llvm/llvm-project/commit/e8723abf43c37aff4d6d9b6ba131e345b74c7798
DIFF: https://github.com/llvm/llvm-project/commit/e8723abf43c37aff4d6d9b6ba131e345b74c7798.diff

LOG: [DSE] Check post-dominance for malloc+memset->calloc transform.

Aiming to address the regression discussed in
https://reviews.llvm.org/D103009.

Differential Revision: https://reviews.llvm.org/D108485

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
    llvm/test/Transforms/DeadStoreElimination/noop-stores.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
index 1bc4a3886dec1..a6b0fce334a7b 100644
--- a/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/DeadStoreElimination.cpp
@@ -1846,7 +1846,7 @@ struct DSEState {
               Func != LibFunc_malloc)
             return false;
           if (Malloc->getOperand(0) == MemSet->getLength()) {
-            if (DT.dominates(Malloc, MemSet) &&
+            if (DT.dominates(Malloc, MemSet) && PDT.dominates(MemSet, Malloc) &&
                 memoryIsNotModifiedBetween(Malloc, MemSet, BatchAA, DL, &DT)) {
               IRBuilder<> IRB(Malloc);
               const auto &DL = Malloc->getModule()->getDataLayout();

diff  --git a/llvm/test/Transforms/DeadStoreElimination/noop-stores.ll b/llvm/test/Transforms/DeadStoreElimination/noop-stores.ll
index 12534b6047c57..38072c159bfe3 100644
--- a/llvm/test/Transforms/DeadStoreElimination/noop-stores.ll
+++ b/llvm/test/Transforms/DeadStoreElimination/noop-stores.ll
@@ -405,14 +405,17 @@ if.end:                                           ; preds = %if.then, %entry
   ret i8* %call
 }
 
+; FIXME: malloc+memset are not currently transformed into calloc unless the
+; memset post-dominates the malloc.
 define float* @pr25892(i64 %size) {
 ; CHECK-LABEL: @pr25892(
 ; CHECK:       entry:
-; CHECK-NEXT:    [[CALL:%.*]] = call i8* @calloc(i64 1, i64 [[SIZE:%.*]])
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @malloc(i64 [[SIZE:%.*]])
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8* [[CALL]], null
 ; CHECK-NEXT:    br i1 [[CMP]], label [[CLEANUP:%.*]], label [[IF_END:%.*]]
 ; CHECK:       if.end:
 ; CHECK-NEXT:    [[BC:%.*]] = bitcast i8* [[CALL]] to float*
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* %call, i8 0, i64 %size, i1 false)
 ; CHECK-NEXT:    br label [[CLEANUP]]
 ; CHECK:       cleanup:
 ; CHECK-NEXT:    [[RETVAL_0:%.*]] = phi float* [ [[BC]], [[IF_END]] ], [ null, [[ENTRY:%.*]] ]
@@ -434,11 +437,13 @@ cleanup:
 define float* @pr25892_with_extra_store(i64 %size) {
 ; CHECK-LABEL: @pr25892_with_extra_store(
 ; CHECK:       entry:
-; CHECK-NEXT:    [[CALL:%.*]] = call i8* @calloc(i64 1, i64 [[SIZE:%.*]])
+; CHECK-NEXT:    [[CALL:%.*]] = call i8* @malloc(i64 [[SIZE:%.*]])
 ; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8* [[CALL]], null
 ; CHECK-NEXT:    br i1 [[CMP]], label [[CLEANUP:%.*]], label [[IF_END:%.*]]
 ; CHECK:       if.end:
 ; CHECK-NEXT:    [[BC:%.*]] = bitcast i8* [[CALL]] to float*
+; CHECK-NEXT:    call void @llvm.memset.p0i8.i64(i8* %call, i8 0, i64 %size, i1 false)
+; CHECK-NEXT:    store i8 0, i8* %call, align 1
 ; CHECK-NEXT:    br label [[CLEANUP]]
 ; CHECK:       cleanup:
 ; CHECK-NEXT:    [[RETVAL_0:%.*]] = phi float* [ [[BC]], [[IF_END]] ], [ null, [[ENTRY:%.*]] ]