[llvm] 42ab5dc - [InstCombine] Handle PHI nodes in isOnlyCopiedFromConstantMemory()

[Nikita Popov via llvm-commits]

Author: Anshil Gandhi
Date: 2023-01-11T17:24:41+01:00
New Revision: 42ab5dc5a5dd6c79476104bdc921afa2a18559cf

URL: https://github.com/llvm/llvm-project/commit/42ab5dc5a5dd6c79476104bdc921afa2a18559cf
DIFF: https://github.com/llvm/llvm-project/commit/42ab5dc5a5dd6c79476104bdc921afa2a18559cf.diff

LOG: [InstCombine] Handle PHI nodes in isOnlyCopiedFromConstantMemory()

As long as the memcpy occurs on a phi input (rather than the phi
output), we can look through phi nodes in
isOnlyCopiedFromConstantMemory().

This is split out of D136201, to only handle the case where the
address spaces are the same, and no pointer rewrite is necessary.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
    llvm/test/Transforms/InstCombine/replace-alloca-phi.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index 8c9b027bd07c..640ba90d9db5 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -72,6 +72,13 @@ isOnlyCopiedFromConstantMemory(AAResults *AA, AllocaInst *V,
         continue;
       }
 
+      if (isa<PHINode>(I)) {
+        // We set IsOffset=true, to forbid the memcpy from occurring after the
+        // phi: If one of the phi operands is not based on the alloca, we
+        // would incorrectly omit a write.
+        Worklist.emplace_back(I, true);
+        continue;
+      }
       if (isa<BitCastInst>(I) || isa<AddrSpaceCastInst>(I)) {
         // If uses of the bitcast are ok, we are ok.
         Worklist.emplace_back(I, IsOffset);

diff  --git a/llvm/test/Transforms/InstCombine/replace-alloca-phi.ll b/llvm/test/Transforms/InstCombine/replace-alloca-phi.ll
index 15baf865100b..4e8aef91d364 100644
--- a/llvm/test/Transforms/InstCombine/replace-alloca-phi.ll
+++ b/llvm/test/Transforms/InstCombine/replace-alloca-phi.ll
@@ -152,13 +152,11 @@ exit:
 define i32 @remove_alloca_ptr_arg(i1 %c, ptr %ptr) {
 ; CHECK-LABEL: @remove_alloca_ptr_arg(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[ALLOCA:%.*]] = alloca [32 x i8], align 1
-; CHECK-NEXT:    call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 1 dereferenceable(32) [[ALLOCA]], ptr noundef nonnull align 16 dereferenceable(32) @g1, i64 32, i1 false)
 ; CHECK-NEXT:    br i1 [[C:%.*]], label [[IF:%.*]], label [[JOIN:%.*]]
 ; CHECK:       if:
 ; CHECK-NEXT:    br label [[JOIN]]
 ; CHECK:       join:
-; CHECK-NEXT:    [[PHI:%.*]] = phi ptr [ [[ALLOCA]], [[IF]] ], [ [[PTR:%.*]], [[ENTRY:%.*]] ]
+; CHECK-NEXT:    [[PHI:%.*]] = phi ptr [ @g1, [[IF]] ], [ [[PTR:%.*]], [[ENTRY:%.*]] ]
 ; CHECK-NEXT:    [[V:%.*]] = load i32, ptr [[PHI]], align 4
 ; CHECK-NEXT:    ret i32 [[V]]
 ;
@@ -269,11 +267,9 @@ join:
 define i32 @phi_loop(i1 %c) {
 ; CHECK-LABEL: @phi_loop(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[ALLOCA:%.*]] = alloca [32 x i8], align 1
-; CHECK-NEXT:    call void @llvm.memcpy.p0.p0.i64(ptr noundef nonnull align 1 dereferenceable(32) [[ALLOCA]], ptr noundef nonnull align 16 dereferenceable(32) @g1, i64 32, i1 false)
 ; CHECK-NEXT:    br label [[LOOP:%.*]]
 ; CHECK:       loop:
-; CHECK-NEXT:    [[PTR:%.*]] = phi ptr [ [[ALLOCA]], [[ENTRY:%.*]] ], [ [[PTR_NEXT:%.*]], [[LOOP]] ]
+; CHECK-NEXT:    [[PTR:%.*]] = phi ptr [ @g1, [[ENTRY:%.*]] ], [ [[PTR_NEXT:%.*]], [[LOOP]] ]
 ; CHECK-NEXT:    [[PTR_NEXT]] = getelementptr i8, ptr [[PTR]], i64 4
 ; CHECK-NEXT:    br i1 [[C:%.*]], label [[EXIT:%.*]], label [[LOOP]]
 ; CHECK:       exit: