When checking that the necessary bits are zero in

order to reduce ((x<<30)>>24) to x<<6, check the
correct bits.  PR 8547.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@118665 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Transforms/InstCombine/InstCombineShifts.cpp b/lib/Transforms/InstCombine/InstCombineShifts.cpp
index 012d238729a4e77af6a7647b50b4ad6e824c0a69..9f7d98ed794d0d17870dc5e69e1c6a94f887936f 100644 (file)
--- a/lib/Transforms/InstCombine/InstCombineShifts.cpp
+++ b/lib/Transforms/InstCombine/InstCombineShifts.cpp
@@ -131,9 +131,9 @@ static bool CanEvaluateShifted(Value *V, unsigned NumBits, bool isLeftShift,
     // We can turn shl(c1)+shr(c2) -> shl(c3)+and(c4), but it isn't
     // profitable unless we know the and'd out bits are already zero.
     if (CI->getZExtValue() > NumBits) {
-      unsigned HighBits = CI->getZExtValue() - NumBits;
+      unsigned LowBits = TypeWidth - CI->getZExtValue();
       if (MaskedValueIsZero(I->getOperand(0),
-                            APInt::getHighBitsSet(TypeWidth, HighBits)))
+                       APInt::getLowBitsSet(TypeWidth, NumBits) << LowBits))
         return true;
     }
       

diff --git a/test/Transforms/InstCombine/pr8547.ll b/test/Transforms/InstCombine/pr8547.ll
new file mode 100644 (file)
index 0000000..f26035c
--- /dev/null
+++ b/test/Transforms/InstCombine/pr8547.ll
@@ -0,0 +1,26 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+; Converting the 2 shifts to SHL 6 without the AND is wrong.  PR 8547.
+
+@g_2 = global i32 0, align 4
+@.str = constant [10 x i8] c"g_2 = %d\0A\00"
+
+declare i32 @printf(i8*, ...)
+
+define i32 @main() nounwind {
+codeRepl:
+  br label %for.cond
+
+for.cond:                                         ; preds = %for.cond, %codeRepl
+  %storemerge = phi i32 [ 0, %codeRepl ], [ 5, %for.cond ]
+  store i32 %storemerge, i32* @g_2, align 4
+  %shl = shl i32 %storemerge, 30
+  %conv2 = lshr i32 %shl, 24
+; CHECK:  %0 = shl i32 %storemerge, 6
+; CHECK:  %conv2 = and i32 %0, 64
+  %tobool = icmp eq i32 %conv2, 0
+  br i1 %tobool, label %for.cond, label %codeRepl2
+
+codeRepl2:                                        ; preds = %for.cond
+  %call = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([10 x i8]* @.str, i64 0, i64 0), i32 %conv2) nounwind
+  ret i32 0
+}
\ No newline at end of file