Modify constraints in `llvm::canReplaceOperandWithVariable`

Summary:
`Instruction::Switch`: only first operand can be set to a non-constant value.
`Instruction::InsertValue` both the first and the second operand can be set to a non-constant value.
`Instruction::Alloca` return true for non-static allocation.

Reviewers: efriedma

Reviewed By: efriedma

Subscribers: srhines, pirama, llvm-commits

Differential Revision: https://reviews.llvm.org/D34905

llvm-svn: 307294

2 files changed, 32 insertions, 2 deletions

diff --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 5127eba3f9a..e4c94acde52 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -2182,12 +2182,18 @@ bool llvm::canReplaceOperandWithVariable(const Instruction *I, unsigned OpIdx) {
   case Instruction::ShuffleVector:
     // Shufflevector masks are constant.
     return OpIdx != 2;
+  case Instruction::Switch:
   case Instruction::ExtractValue:
-  case Instruction::InsertValue:
     // All operands apart from the first are constant.
     return OpIdx == 0;
+  case Instruction::InsertValue:
+    // All operands apart from the first and the second are constant.
+    return OpIdx < 2;
   case Instruction::Alloca:
-    return false;
+    // Static allocas (constant size in the entry block) are handled by
+    // prologue/epilogue insertion so they're free anyway. We definitely don't
+    // want to make them non-constant.
+    return !dyn_cast<AllocaInst>(I)->isStaticAlloca();
   case Instruction::GetElementPtr:
     if (OpIdx == 0)
       return true;
diff --git a/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll b/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
index 0f7bfa8516c..513da477607 100644
--- a/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
+++ b/llvm/test/Transforms/SimplifyCFG/sink-common-code.ll
@@ -818,6 +818,30 @@ merge:
 ; CHECK: right:
 ; CHECK-NEXT:   %val1 = call i32 @call_target() [ "deopt"(i32 20) ]
 
+%T = type {i32, i32}
+
+define i32 @test_insertvalue(i1 zeroext %flag, %T %P) {
+entry:
+  br i1 %flag, label %if.then, label %if.else
+
+if.then:
+  %t1 = insertvalue %T %P, i32 0, 0
+  br label %if.end
+
+if.else:
+  %t2 = insertvalue %T %P, i32 1, 0
+  br label %if.end
+
+if.end:
+  %t = phi %T [%t1, %if.then], [%t2, %if.else]
+  ret i32 1
+}
+
+; CHECK-LABEL: @test_insertvalue
+; CHECK: select
+; CHECK: insertvalue
+; CHECK-NOT: insertvalue
+
 ; CHECK: ![[TBAA]] = !{![[TYPE:[0-9]]], ![[TYPE]], i64 0}
 ; CHECK: ![[TYPE]] = !{!"float", ![[TEXT:[0-9]]]}
 ; CHECK: ![[TEXT]] = !{!"an example type tree"}