Fix bug in PR454 resolution. Added new test case.

This fixes llvmAsmParser.cpp miscompile by llvm on PowerPC Darwin.

llvm-svn: 31053

llvm/lib/Transforms/Scalar/InstructionCombining.cpp

@@ -4785,7 +4785,21 @@ Instruction *InstCombiner::visitSetCondInstWithCastAndCast(SetCondInst &SCI) {
     Constant *Res = ConstantExpr::getCast(CI, SrcTy);
 
     if (ConstantExpr::getCast(Res, DestTy) == CI) {
-      RHSCIOp = Res;
+      // Make sure that src sign and dest sign match. For example,
+      //
+      // %A = cast short %X to uint
+      // %B = setgt uint %A, 1330
+      //
+      // It is incorrect to transformt this into 
+      //
+      // %B = setgt short %X, 1330 
+      // 
+      // because %A may have negative value. 
+      // However, it is OK if SrcTy is bool. See cast-set.ll testcase.
+      if (isSignSrc == isSignDest || SrcTy == Type::BoolTy)
+        RHSCIOp = Res;
+      else
+        return 0;
     } else {
       // If the value cannot be represented in the shorter type, we cannot emit
       // a simple comparison.

llvm/test/Regression/Transforms/InstCombine/2004-11-27-SetCCForCastLargerAndConstant.ll

@@ -31,12 +31,6 @@ bool %lt_signed_to_large_negative(sbyte %SB) {
   ret bool %C
 }
 
-bool %lt_signed_to_small_unsigned(sbyte %SB) {
-  %Y = cast sbyte %SB to uint		; <uint> [#uses=1]
-  %C = setlt uint %Y, 17		; <bool> [#uses=1]
-  ret bool %C
-}
-
 bool %lt_signed_to_small_signed(sbyte %SB) {
   %Y = cast sbyte %SB to int
   %C = setlt int %Y, 17
@@ -73,12 +67,6 @@ bool %lt_unsigned_to_small_unsigned(ubyte %SB) {
   ret bool %C
 }
 
-bool %lt_unsigned_to_small_signed(ubyte %SB) {
-  %Y = cast ubyte %SB to int
-  %C = setlt int %Y, 17
-  ret bool %C
-}
-
 bool %lt_unsigned_to_small_negative(ubyte %SB) {
   %Y = cast ubyte %SB to int
   %C = setlt int %Y, -17
@@ -103,12 +91,6 @@ bool %gt_signed_to_large_negative(sbyte %SB) {
   ret bool %C
 }
 
-bool %gt_signed_to_small_unsigned(sbyte %SB) {
-  %Y = cast sbyte %SB to uint		; <uint> [#uses=1]
-  %C = setgt uint %Y, 17		; <bool> [#uses=1]
-  ret bool %C
-}
-
 bool %gt_signed_to_small_signed(sbyte %SB) {
   %Y = cast sbyte %SB to int
   %C = setgt int %Y, 17
@@ -145,12 +127,6 @@ bool %gt_unsigned_to_small_unsigned(ubyte %SB) {
   ret bool %C
 }
 
-bool %gt_unsigned_to_small_signed(ubyte %SB) {
-  %Y = cast ubyte %SB to int
-  %C = setgt int %Y, 17
-  ret bool %C
-}
-
 bool %gt_unsigned_to_small_negative(ubyte %SB) {
   %Y = cast ubyte %SB to int
   %C = setgt int %Y, -17

llvm/test/Regression/Transforms/InstCombine/2006-10-19-SignedToUnsignedCastAndConst.ll

@@ -0,0 +1,8 @@
+; This test case is reduced from llvmAsmParser.cpp
+; The optimizer should not remove the cast here.
+; RUN: llvm-as %s -o - | opt -instcombine | llvm-dis | grep 'cast.*int'
+bool %test(short %X) {
+%A = cast short %X to uint
+%B = setgt uint %A, 1330
+ret bool %B
+}