[GVNSink] Fix incorrect codegen with respect to GEPs #85333

[hiraditya]

As mentioned in #68882 and https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699

Gep arithmetic isn't consistent with different types. GVNSink didn't realize this and sank all geps as long as their operands can be wired via PHIs
in a post-dominator.

Fixes: #85333
Reapply: #88440 after fixing the non-determinism issues in #90995

[llvmbot]

@llvm/pr-subscribers-llvm-transforms

Author: AdityaK (hiraditya)

Changes

As mentioned in #68882 and https://discourse.llvm.org/t/rfc-replacing-getelementptr-with-ptradd/68699

Gep arithmetic isn't consistent with different types. GVNSink didn't realize this and sank all geps as long as their operands can be wired via PHIs
in a post-dominator.

Fixes: #85333
Reapply: #88440 after fixing the non-determinism issues in #90995

---

Full diff: https://github.com/llvm/llvm-project/pull/92047.diff

2 Files Affected:

• (modified) llvm/lib/Transforms/Scalar/GVNSink.cpp (+4-5)
• (added) llvm/test/Transforms/GVNSink/different-gep-types.ll (+101)

diff --git a/llvm/lib/Transforms/Scalar/GVNSink.cpp b/llvm/lib/Transforms/Scalar/GVNSink.cpp
index 95a4c644a91ad..7a183e4d3aa8f 100644
--- a/llvm/lib/Transforms/Scalar/GVNSink.cpp
+++ b/llvm/lib/Transforms/Scalar/GVNSink.cpp
@@ -763,12 +763,11 @@ GVNSink::analyzeInstructionForSinking(LockstepReverseIterator &LRI,
   // try and continue making progress.
   Instruction *I0 = NewInsts[0];
 
-  // If all instructions that are going to participate don't have the same
-  // number of operands, we can't do any useful PHI analysis for all operands.
-  auto hasDifferentNumOperands = [&I0](Instruction *I) {
-    return I->getNumOperands() != I0->getNumOperands();
+  auto isNotSameOperation = [&I0](Instruction *I) {
+    return !I0->isSameOperationAs(I);
   };
-  if (any_of(NewInsts, hasDifferentNumOperands))
+
+  if (any_of(NewInsts, isNotSameOperation))
     return std::nullopt;
 
   for (unsigned OpNum = 0, E = I0->getNumOperands(); OpNum != E; ++OpNum) {
diff --git a/llvm/test/Transforms/GVNSink/different-gep-types.ll b/llvm/test/Transforms/GVNSink/different-gep-types.ll
new file mode 100644
index 0000000000000..659be51cc56ee
--- /dev/null
+++ b/llvm/test/Transforms/GVNSink/different-gep-types.ll
@@ -0,0 +1,101 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 4
+; RUN: opt -passes=gvn-sink -S %s | FileCheck %s
+
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+
+%"struct.std::pair" = type <{ i32, %struct.substruct, [2 x i8] }>
+%struct.substruct = type { i8, i8 }
+%"struct.std::random_access_iterator_tag" = type { i8 }
+
+; Check that gep is not sunk as they are of different types.
+define void @bar(ptr noundef nonnull align 4 dereferenceable(4) %__i, i32 noundef %__n) {
+; CHECK-LABEL: define void @bar(
+; CHECK-SAME: ptr noundef nonnull align 4 dereferenceable(4) [[__I:%.*]], i32 noundef [[__N:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[__N]], 1
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[__I]], align 4
+; CHECK-NEXT:    [[INCDEC_PTR4:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i32 -8
+; CHECK-NEXT:    br label [[IF_END6:%.*]]
+; CHECK:       if.else:
+; CHECK-NEXT:    [[TMP1:%.*]] = load ptr, ptr [[__I]], align 4
+; CHECK-NEXT:    [[ADD_PTR:%.*]] = getelementptr inbounds %"struct.std::pair", ptr [[TMP1]], i32 [[__N]]
+; CHECK-NEXT:    br label [[IF_END6]]
+; CHECK:       if.end6:
+; CHECK-NEXT:    [[INCDEC_PTR_SINK:%.*]] = phi ptr [ [[INCDEC_PTR4]], [[IF_THEN]] ], [ [[ADD_PTR]], [[IF_ELSE]] ]
+; CHECK-NEXT:    store ptr [[INCDEC_PTR_SINK]], ptr [[__I]], align 4
+; CHECK-NEXT:    ret void
+;
+entry:
+  %cmp = icmp eq i32 %__n, 1
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %3 = load ptr, ptr %__i, align 4
+  %incdec.ptr4 = getelementptr inbounds i8, ptr %3, i32 -8
+  br label %if.end6
+
+if.else:
+  %4 = load ptr, ptr %__i, align 4
+  %add.ptr = getelementptr inbounds %"struct.std::pair", ptr %4, i32 %__n
+  br label %if.end6
+
+if.end6:
+  %incdec.ptr.sink = phi ptr [ %incdec.ptr4, %if.then ], [ %add.ptr, %if.else ]
+  store ptr %incdec.ptr.sink, ptr %__i, align 4
+  ret void
+}
+
+; Check that load,gep, and store are all sunk as they are safe to do.
+define void @foo(ptr noundef nonnull align 4 dereferenceable(4) %__i, i32 noundef %__n) {
+; CHECK-LABEL: define void @foo(
+; CHECK-SAME: ptr noundef nonnull align 4 dereferenceable(4) [[__I:%.*]], i32 noundef [[__N:%.*]]) {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i32 [[__N]], 1
+; CHECK-NEXT:    br i1 [[CMP]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
+; CHECK:       if.then:
+; CHECK-NEXT:    br label [[IF_END6:%.*]]
+; CHECK:       if.else:
+; CHECK-NEXT:    [[CMP2:%.*]] = icmp eq i32 [[__N]], -1
+; CHECK-NEXT:    br i1 [[CMP2]], label [[IF_THEN3:%.*]], label [[IF_ELSE5:%.*]]
+; CHECK:       if.then3:
+; CHECK-NEXT:    br label [[IF_END6]]
+; CHECK:       if.else5:
+; CHECK-NEXT:    br label [[IF_END6]]
+; CHECK:       if.end6:
+; CHECK-NEXT:    [[DOTSINK1:%.*]] = phi i32 [ -4, [[IF_ELSE5]] ], [ -8, [[IF_THEN3]] ], [ 8, [[IF_THEN]] ]
+; CHECK-NEXT:    [[TMP0:%.*]] = load ptr, ptr [[__I]], align 4
+; CHECK-NEXT:    [[INCDEC_PTR:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i32 [[DOTSINK1]]
+; CHECK-NEXT:    store ptr [[INCDEC_PTR]], ptr [[__I]], align 4
+; CHECK-NEXT:    ret void
+;
+entry:
+  %cmp = icmp eq i32 %__n, 1
+  br i1 %cmp, label %if.then, label %if.else
+
+if.then:
+  %1 = load ptr, ptr %__i, align 4
+  %incdec.ptr = getelementptr inbounds i8, ptr %1, i32 8
+  store ptr %incdec.ptr, ptr %__i, align 4
+  br label %if.end6
+
+if.else:
+  %cmp2 = icmp eq i32 %__n, -1
+  br i1 %cmp2, label %if.then3, label %if.else5
+
+if.then3:
+  %3 = load ptr, ptr %__i, align 4
+  %incdec.ptr4 = getelementptr inbounds i8, ptr %3, i32 -8
+  store ptr %incdec.ptr4, ptr %__i, align 4
+  br label %if.end6
+
+if.else5:
+  %4 = load ptr, ptr %__i, align 4
+  %add.ptr = getelementptr inbounds i8, ptr %4, i32 -4
+  store ptr %add.ptr, ptr %__i, align 4
+  br label %if.end6
+
+if.end6:
+  ret void
+}

[nikic]

LGTM