Tell the NCG that XOR foo, foo does *not* read foo

[ghc-hetmet.git] / compiler / nativeGen / RegAllocInfo.hs

diff --git a/compiler/nativeGen/RegAllocInfo.hs b/compiler/nativeGen/RegAllocInfo.hs
index df74218..d526641 100644 (file)
--- a/compiler/nativeGen/RegAllocInfo.hs
+++ b/compiler/nativeGen/RegAllocInfo.hs
@@ -156,6 +156,8 @@ regUsage instr = case instr of
     IDIV   sz op       -> mkRU (eax:edx:use_R op) [eax,edx]
     AND    sz src dst  -> usageRM src dst
     OR     sz src dst  -> usageRM src dst
+    XOR    sz (OpReg src) (OpReg dst)
+        | src == dst    -> mkRU [] [dst]
     XOR    sz src dst  -> usageRM src dst
     NOT    sz op       -> usageM op
     NEGI   sz op       -> usageM op