1 files changed, 18 insertions, 5 deletions
diff --git a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
index 4909d18d967..91c906c25ec 100644
--- a/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
+++ b/llvm/lib/Target/X86/X86ISelDAGToDAG.cpp
@@ -3392,8 +3392,11 @@ void X86DAGToDAGISel::Select(SDNode *Node) {
     SDValue N0 = Node->getOperand(0);
     SDValue N1 = Node->getOperand(1);
 
-    if (N0.getOpcode() == ISD::TRUNCATE && N0.hasOneUse() &&
-        hasNoSignedComparisonUses(Node))
+    // Save the original VT of the compare.
+    MVT CmpVT = N0.getSimpleValueType();
+
+    // We can peek through truncates, but we need to be careful below.
+    if (N0.getOpcode() == ISD::TRUNCATE && N0.hasOneUse())
       N0 = N0.getOperand(0);
 
     // Look for (X86cmp (and $op, $imm), 0) and see if we can convert it to
@@ -3411,14 +3414,21 @@ void X86DAGToDAGISel::Select(SDNode *Node) {
       int SubRegOp;
       unsigned Op;
 
+      // For each of these checks we need to be careful if the sign flag is
+      // being used. It is only safe to use the sign flag in two conditions,
+      // either the sign bit in the shrunken mask is zero or the final test
+      // size is equal to the original compare size.
+
       if (isUInt<8>(Mask) &&
-          (!(Mask & 0x80) || hasNoSignedComparisonUses(Node))) {
+          (!(Mask & 0x80) || CmpVT == MVT::i8 ||
+           hasNoSignedComparisonUses(Node))) {
         // For example, convert "testl %eax, $8" to "testb %al, $8"
         VT = MVT::i8;
         SubRegOp = X86::sub_8bit;
         Op = X86::TEST8ri;
       } else if (OptForMinSize && isUInt<16>(Mask) &&
-                 (!(Mask & 0x8000) || hasNoSignedComparisonUses(Node))) {
+                 (!(Mask & 0x8000) || CmpVT == MVT::i16 ||
+                  hasNoSignedComparisonUses(Node))) {
         // For example, "testl %eax, $32776" to "testw %ax, $32776".
         // NOTE: We only want to form TESTW instructions if optimizing for
         // min size. Otherwise we only save one byte and possibly get a length
@@ -3427,7 +3437,8 @@ void X86DAGToDAGISel::Select(SDNode *Node) {
         SubRegOp = X86::sub_16bit;
         Op = X86::TEST16ri;
       } else if (isUInt<32>(Mask) && N0.getValueType() != MVT::i16 &&
-                 (!(Mask & 0x80000000) || hasNoSignedComparisonUses(Node))) {
+                 (!(Mask & 0x80000000) || CmpVT == MVT::i32 ||
+                  hasNoSignedComparisonUses(Node))) {
         // For example, "testq %rax, $268468232" to "testl %eax, $268468232".
         // NOTE: We only want to run that transform if N0 is 32 or 64 bits.
         // Otherwize, we find ourselves in a position where we have to do
@@ -3441,6 +3452,8 @@ void X86DAGToDAGISel::Select(SDNode *Node) {
         break;
       }
 
+      // FIXME: We should be able to fold loads here.
+
       SDValue Imm = CurDAG->getTargetConstant(Mask, dl, VT);
       SDValue Reg = N0.getOperand(0);