[llvm] edd1360 - [InstCombine] Preserve metadata from orig load in select fold. (#115605)

[via llvm-commits]

Author: Florian Hahn
Date: 2025-01-16T22:44:40Z
New Revision: edd1360208b2c4dc60d81b525d6e59d9fb491c05

URL: https://github.com/llvm/llvm-project/commit/edd1360208b2c4dc60d81b525d6e59d9fb491c05
DIFF: https://github.com/llvm/llvm-project/commit/edd1360208b2c4dc60d81b525d6e59d9fb491c05.diff

LOG: [InstCombine] Preserve metadata from orig load in select fold. (#115605)

When replacing load with a select on the address with a select and 2
loads of the values, copy poison-generating metadata from the original
load to the newly created loads, which are placed at the same place as
the original loads. We cannot copy metadata that may trigger UB.

PR: https://github.com/llvm/llvm-project/pull/115605

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
    llvm/test/Transforms/InstCombine/loadstore-metadata.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
index f87a4a58470402..61f1c17592e966 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineLoadStoreAlloca.cpp
@@ -1060,6 +1060,10 @@ Instruction *InstCombinerImpl::visitLoadInst(LoadInst &LI) {
         V1->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
         V2->setAlignment(Alignment);
         V2->setAtomic(LI.getOrdering(), LI.getSyncScopeID());
+        // It is safe to copy any metadata that does not trigger UB. Copy any
+        // poison-generating metadata.
+        V1->copyMetadata(LI, Metadata::PoisonGeneratingIDs);
+        V2->copyMetadata(LI, Metadata::PoisonGeneratingIDs);
         return SelectInst::Create(SI->getCondition(), V1, V2);
       }
 

diff  --git a/llvm/test/Transforms/InstCombine/loadstore-metadata.ll b/llvm/test/Transforms/InstCombine/loadstore-metadata.ll
index 1aae4ed1eb2b57..5a977882504cef 100644
--- a/llvm/test/Transforms/InstCombine/loadstore-metadata.ll
+++ b/llvm/test/Transforms/InstCombine/loadstore-metadata.ll
@@ -186,12 +186,12 @@ entry:
   ret i32 %c
 }
 
-; FIXME: Should preserve none-UB metadata on loads.
+; Preserve none-UB metadata on loads.
 define ptr @preserve_load_metadata_after_select_transform1(i1 %c, ptr dereferenceable(8) %a, ptr dereferenceable(8) %b) {
 ; CHECK-LABEL: @preserve_load_metadata_after_select_transform1(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[B_VAL:%.*]] = load ptr, ptr [[B:%.*]], align 1
-; CHECK-NEXT:    [[A_VAL:%.*]] = load ptr, ptr [[A:%.*]], align 1
+; CHECK-NEXT:    [[B_VAL:%.*]] = load ptr, ptr [[B:%.*]], align 1, !nonnull [[META6]], !align [[META8]]
+; CHECK-NEXT:    [[A_VAL:%.*]] = load ptr, ptr [[A:%.*]], align 1, !nonnull [[META6]], !align [[META8]]
 ; CHECK-NEXT:    [[L_SEL:%.*]] = select i1 [[C:%.*]], ptr [[B_VAL]], ptr [[A_VAL]]
 ; CHECK-NEXT:    ret ptr [[L_SEL]]
 ;
@@ -201,12 +201,12 @@ entry:
   ret ptr %l.sel
 }
 
-; FIXME: Should preserve none-UB metadata on loads.
+; Preserve none-UB metadata on loads.
 define i32 @preserve_load_metadata_after_select_transform_range(i1 %c, ptr dereferenceable(8) %a, ptr dereferenceable(8) %b) {
 ; CHECK-LABEL: @preserve_load_metadata_after_select_transform_range(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[B_VAL:%.*]] = load i32, ptr [[B:%.*]], align 1
-; CHECK-NEXT:    [[A_VAL:%.*]] = load i32, ptr [[A:%.*]], align 1
+; CHECK-NEXT:    [[B_VAL:%.*]] = load i32, ptr [[B:%.*]], align 1, !range [[RNG10:![0-9]+]]
+; CHECK-NEXT:    [[A_VAL:%.*]] = load i32, ptr [[A:%.*]], align 1, !range [[RNG10]]
 ; CHECK-NEXT:    [[L_SEL:%.*]] = select i1 [[C:%.*]], i32 [[B_VAL]], i32 [[A_VAL]]
 ; CHECK-NEXT:    ret i32 [[L_SEL]]
 ;
@@ -294,7 +294,7 @@ define double @preserve_load_metadata_after_select_transform_metadata_missing_4(
 ; CHECK-LABEL: @preserve_load_metadata_after_select_transform_metadata_missing_4(
 ; CHECK-NEXT:  entry:
 ; CHECK-NEXT:    [[L_A:%.*]] = load double, ptr [[A:%.*]], align 8, !tbaa [[TBAA0]], !alias.scope [[META3]], !noalias [[META3]], !llvm.access.group [[META6]]
-; CHECK-NEXT:    [[L_B:%.*]] = load double, ptr [[B:%.*]], align 8, !tbaa [[TBAA0]], !alias.scope [[META10:![0-9]+]], !noalias [[META10]], !llvm.access.group [[ACC_GRP13:![0-9]+]]
+; CHECK-NEXT:    [[L_B:%.*]] = load double, ptr [[B:%.*]], align 8, !tbaa [[TBAA0]], !alias.scope [[META11:![0-9]+]], !noalias [[META11]], !llvm.access.group [[ACC_GRP14:![0-9]+]]
 ; CHECK-NEXT:    [[CMP_I:%.*]] = fcmp fast olt double [[L_A]], [[L_B]]
 ; CHECK-NEXT:    [[L_SEL:%.*]] = select i1 [[CMP_I]], double [[L_B]], double [[L_A]]
 ; CHECK-NEXT:    ret double [[L_SEL]]
@@ -337,8 +337,9 @@ entry:
 ; CHECK: [[META7]] = !{i32 1}
 ; CHECK: [[META8]] = !{i64 8}
 ; CHECK: [[ACC_GRP9]] = distinct !{}
-; CHECK: [[META10]] = !{[[META11:![0-9]+]]}
-; CHECK: [[META11]] = distinct !{[[META11]], [[META12:![0-9]+]]}
-; CHECK: [[META12]] = distinct !{[[META12]]}
-; CHECK: [[ACC_GRP13]] = distinct !{}
+; CHECK: [[RNG10]] = !{i32 0, i32 42}
+; CHECK: [[META11]] = !{[[META12:![0-9]+]]}
+; CHECK: [[META12]] = distinct !{[[META12]], [[META13:![0-9]+]]}
+; CHECK: [[META13]] = distinct !{[[META13]]}
+; CHECK: [[ACC_GRP14]] = distinct !{}
 ;.