[llvm-commits] [llvm] r152006 - in /llvm/trunk: lib/Transforms/Scalar/GVN.cpp test/Transforms/GVN/condprop.ll

[Duncan Sands]

Author: baldrick
Date: Sun Mar  4 07:25:19 2012
New Revision: 152006

URL: http://llvm.org/viewvc/llvm-project?rev=152006&view=rev
Log:
Nick pointed out on IRC that GVN's propagateEquality wasn't propagating
equalities into phi node operands for which the equality is known to
hold in the incoming basic block.  That's because replaceAllDominatedUsesWith
wasn't handling phi nodes correctly in general (that this didn't give wrong
results was just luck: the specific way GVN uses replaceAllDominatedUsesWith
precluded wrong changes to phi nodes).

Modified:
    llvm/trunk/lib/Transforms/Scalar/GVN.cpp
    llvm/trunk/test/Transforms/GVN/condprop.ll

Modified: llvm/trunk/lib/Transforms/Scalar/GVN.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/GVN.cpp?rev=152006&r1=152005&r2=152006&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/GVN.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/GVN.cpp Sun Mar  4 07:25:19 2012
@@ -1953,7 +1953,17 @@
   for (Value::use_iterator UI = From->use_begin(), UE = From->use_end();
        UI != UE; ) {
     Use &U = (UI++).getUse();
-    if (DT->dominates(Root, cast<Instruction>(U.getUser())->getParent())) {
+
+    // If From occurs as a phi node operand then the use implicitly lives in the
+    // corresponding incoming block.  Otherwise it is the block containing the
+    // user that must be dominated by Root.
+    BasicBlock *UsingBlock;
+    if (PHINode *PN = dyn_cast<PHINode>(U.getUser()))
+      UsingBlock = PN->getIncomingBlock(U);
+    else
+      UsingBlock = cast<Instruction>(U.getUser())->getParent();
+
+    if (DT->dominates(Root, UsingBlock)) {
       U.set(To);
       ++Count;
     }

Modified: llvm/trunk/test/Transforms/GVN/condprop.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/GVN/condprop.ll?rev=152006&r1=152005&r2=152006&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/GVN/condprop.ll (original)
+++ llvm/trunk/test/Transforms/GVN/condprop.ll Sun Mar  4 07:25:19 2012
@@ -232,3 +232,20 @@
 next2:
   ret i32 0
 }
+
+; CHECK: @test12
+define i32 @test12(i32 %x) {
+  %cmp = icmp eq i32 %x, 0
+  br i1 %cmp, label %cond_true, label %cond_false
+
+cond_true:
+  br label %ret
+
+cond_false:
+  br label %ret
+
+ret:
+  %res = phi i32 [ %x, %cond_true ], [ %x, %cond_false ]
+; CHECK: %res = phi i32 [ 0, %cond_true ], [ %x, %cond_false ]
+  ret i32 %res
+}