[PATCH] D24542: Make vector operation with variable index unsafe to speculate

[Matt Arsenault via llvm-commits]

arsenm created this revision.
arsenm added a subscriber: llvm-commits.
Herald added a subscriber: wdng.

A branch condition could be guarding an out of bounds access of the vector.

https://reviews.llvm.org/D24542

Files:
  lib/Analysis/ValueTracking.cpp
  test/Transforms/SimplifyCFG/speculate-vector-ops.ll

Index: test/Transforms/SimplifyCFG/speculate-vector-ops.ll
===================================================================
--- test/Transforms/SimplifyCFG/speculate-vector-ops.ll
+++ test/Transforms/SimplifyCFG/speculate-vector-ops.ll
@@ -57,4 +57,40 @@
   br label %return
 }
 
+; CHECK-LABEL: @no_speculate_extractelement_varindex(
+; CHECK: br i1 %cmp
+; CHECK: extractelement
+; CHECK: phi
+define i32 @no_speculate_extractelement_varindex(i32 %c, i32 %idx) #0 {
+entry:
+  %cmp = icmp eq i32 %c, 0
+  br i1 %cmp, label %a, label %b
+
+a:
+  %x = extractelement <4 x i32> undef, i32 %idx
+  br label %b
+
+b:
+  %phi = phi i32 [ 0, %entry], [ %x, %a ]
+  ret i32 %phi
+}
+
+; CHECK-LABEL: @no_speculate_insertelement_varindex(
+; CHECK: br i1 %cmp
+; CHECK: insertelement
+; CHECK: phi
+define <4 x i32> @no_speculate_insertelement_varindex(i32 %c, i32 %idx) #0 {
+entry:
+  %cmp = icmp eq i32 %c, 0
+  br i1 %cmp, label %a, label %b
+
+a:
+  %x = insertelement <4 x i32> undef, i32 8, i32 %idx
+  br label %b
+
+b:
+  %phi = phi <4 x i32> [ zeroinitializer, %entry], [ %x, %a ]
+  ret <4 x i32> %phi
+}
+
 attributes #0 = { nounwind }
Index: lib/Analysis/ValueTracking.cpp
===================================================================
--- lib/Analysis/ValueTracking.cpp
+++ lib/Analysis/ValueTracking.cpp
@@ -3235,6 +3235,10 @@
     return false; // The called function could have undefined behavior or
                   // side-effects, even if marked readnone nounwind.
   }
+  case Instruction::ExtractElement:
+    return isa<Constant>(Inst->getOperand(1));
+  case Instruction::InsertElement:
+    return isa<Constant>(Inst->getOperand(2));
   case Instruction::VAArg:
   case Instruction::Alloca:
   case Instruction::Invoke:


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