R600: Add comment clariying use of sext for result of MUL_U24

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@206501 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/R600/AMDGPUISelLowering.cpp b/lib/Target/R600/AMDGPUISelLowering.cpp
index 2e7e7584a9d1e24ebaee57104fbd8cd959a1cdcf..c1a607d25e376f23747ea2c6f167bdb17852ba9d 100644 (file)
--- a/lib/Target/R600/AMDGPUISelLowering.cpp
+++ b/lib/Target/R600/AMDGPUISelLowering.cpp
@@ -1158,6 +1158,8 @@ SDValue AMDGPUTargetLowering::PerformDAGCombine(SDNode *N,
         break;
       }
 
+      // We need to use sext even for MUL_U24, because MUL_U24 is used
+      // for signed multiply of 8 and 16-bit types.
       SDValue Reg = DAG.getSExtOrTrunc(Mul, DL, VT);
 
       return Reg;