[llvm] r210986 - LegalizeDAG: make sure cast is unsigned before using FP_TO_UINT.

Tim Northover tnorthover at apple.com
Sun Jun 15 02:27:20 PDT 2014

Author: tnorthover
Date: Sun Jun 15 04:27:20 2014
New Revision: 210986

URL: http://llvm.org/viewvc/llvm-project?rev=210986&view=rev
LegalizeDAG: make sure cast is unsigned before using FP_TO_UINT.

It's valid to use FP_TO_SINT when asking for a smaller type (e.g. all
"unsigned int16" values fit into a "signed int32"), but the reverse
isn't true.

Unfortunately, I'm not actually aware of any architecture with
asymmetric FP_TO_SINT and FP_TO_UINT handling and the logic happens to
work in the symmetric case, so I can't actually write a test for this.


Modified: llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp?rev=210986&r1=210985&r2=210986&view=diff
--- llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp (original)
+++ llvm/trunk/lib/CodeGen/SelectionDAG/LegalizeDAG.cpp Sun Jun 15 04:27:20 2014
@@ -2650,12 +2650,15 @@ SDValue SelectionDAGLegalize::PromoteLeg
     NewOutTy = (MVT::SimpleValueType)(NewOutTy.getSimpleVT().SimpleTy+1);
     assert(NewOutTy.isInteger() && "Ran out of possibilities!");
+    // A larger signed type can hold all unsigned values of the requested type,
+    // so using FP_TO_SINT is valid
     if (TLI.isOperationLegalOrCustom(ISD::FP_TO_SINT, NewOutTy)) {
       OpToUse = ISD::FP_TO_SINT;
-    if (TLI.isOperationLegalOrCustom(ISD::FP_TO_UINT, NewOutTy)) {
+    // However, if the value may be < 0.0, we *must* use some FP_TO_SINT.
+    if (!isSigned && TLI.isOperationLegalOrCustom(ISD::FP_TO_UINT, NewOutTy)) {
       OpToUse = ISD::FP_TO_UINT;

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