Fix a bug in the ComputeMaskedBits logic for multiply.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@50793 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
index 3e75f7b3056fb9206ce6b865cff48e55d4e3052b..3d5a126df1b835b3635b1dc80cd89231ef361196 100644 (file)
--- a/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
+++ b/lib/CodeGen/SelectionDAG/SelectionDAG.cpp
@@ -1244,8 +1244,8 @@ void SelectionDAG::ComputeMaskedBits(SDOperand Op, const APInt &Mask,
     unsigned TrailZ = KnownZero.countTrailingOnes() +
                       KnownZero2.countTrailingOnes();
     unsigned LeadZ =  std::max(KnownZero.countLeadingOnes() +
-                               KnownZero2.countLeadingOnes() +
-                               1, BitWidth) - BitWidth;
+                               KnownZero2.countLeadingOnes(),
+                               BitWidth) - BitWidth;
 
     TrailZ = std::min(TrailZ, BitWidth);
     LeadZ = std::min(LeadZ, BitWidth);

diff --git a/lib/Transforms/Scalar/InstructionCombining.cpp b/lib/Transforms/Scalar/InstructionCombining.cpp
index 2afa6c51622c236f383a3eaa574138933a085654..66d5326b9f3427fe01a80b56cb803add728820a9 100644 (file)
--- a/lib/Transforms/Scalar/InstructionCombining.cpp
+++ b/lib/Transforms/Scalar/InstructionCombining.cpp
@@ -767,8 +767,8 @@ void InstCombiner::ComputeMaskedBits(Value *V, const APInt &Mask,
     unsigned TrailZ = KnownZero.countTrailingOnes() +
                       KnownZero2.countTrailingOnes();
     unsigned LeadZ =  std::max(KnownZero.countLeadingOnes() +
-                               KnownZero2.countLeadingOnes() +
-                               1, BitWidth) - BitWidth;
+                               KnownZero2.countLeadingOnes(),
+                               BitWidth) - BitWidth;
 
     TrailZ = std::min(TrailZ, BitWidth);
     LeadZ = std::min(LeadZ, BitWidth);

diff --git a/test/Transforms/InstCombine/mul-masked-bits.ll b/test/Transforms/InstCombine/mul-masked-bits.ll
new file mode 100644 (file)
index 0000000..9b0a5bf
--- /dev/null
+++ b/test/Transforms/InstCombine/mul-masked-bits.ll
@@ -0,0 +1,10 @@
+; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep ashr
+
+define i32 @foo(i32 %x, i32 %y) {
+  %a = and i32 %x, 7
+  %b = and i32 %y, 7
+  %c = mul i32 %a, %b
+  %d = shl i32 %c, 26
+  %e = ashr i32 %d, 26
+  ret i32 %e
+}