The DAGCombiner was threading select over pairs of extending loads even

if the extension types were not the same.  The result was that if you
fed a select with sext and zext loads, as in the testcase, then it
would get turned into a zext (or sext) of the select, which is wrong
in the cases when it should have been an sext (resp. zext).  Reported
and diagnosed by Sebastien Deldon.

llvm-svn: 119728

2 files changed, 20 insertions, 0 deletions

diff --git a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
index 1a0f503378d..53b449309c7 100644
--- a/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
+++ b/llvm/lib/CodeGen/SelectionDAG/DAGCombiner.cpp
@@ -6658,6 +6658,11 @@ bool DAGCombiner::SimplifySelectOps(SDNode *TheSelect, SDValue LHS,
         LLD->isVolatile() || RLD->isVolatile() ||
         // If this is an EXTLOAD, the VT's must match.
         LLD->getMemoryVT() != RLD->getMemoryVT() ||
+        // If this is an EXTLOAD, the kind of extension must match.
+        (LLD->getExtensionType() != RLD->getExtensionType() &&
+         // The only exception is if one of the extensions is anyext.
+         LLD->getExtensionType() != ISD::EXTLOAD &&
+         RLD->getExtensionType() != ISD::EXTLOAD) ||
         // FIXME: this discards src value information.  This is
         // over-conservative. It would be beneficial to be able to remember
         // both potential memory locations.  Since we are discarding
diff --git a/llvm/test/CodeGen/X86/2010-11-18-SelectOfExtload.ll b/llvm/test/CodeGen/X86/2010-11-18-SelectOfExtload.ll
new file mode 100644
index 00000000000..a1074b6b8f3
--- /dev/null
+++ b/llvm/test/CodeGen/X86/2010-11-18-SelectOfExtload.ll
@@ -0,0 +1,15 @@
+; RUN: llc < %s -march=x86 | FileCheck %s
+; Both values were being zero extended.
+@u = external global i8
+@s = external global i8
+define i32 @foo(i1 %cond) {
+; CHECK: @foo
+  %u_base = load i8* @u
+  %u_val = zext i8 %u_base to i32
+; CHECK: movzbl
+; CHECK: movsbl
+  %s_base = load i8* @s
+  %s_val = sext i8 %s_base to i32
+  %val = select i1 %cond, i32 %u_val, i32 %s_val
+  ret i32 %val
+}