[InstCombine] In foldSelectICmpAnd, if we need to to truncate from the 'and' type to the 'select' type, do it after shifting right instead of just bailing.
Previously we were always trying to emit the zext or truncate before any shift. This meant if the 'and' mask was larger than the size of the truncate we would skip the transformation.
Now we shift the result of the and right first leaving the bit within the range of the truncate.
This matches what we are doing in foldSelectICmpAndOr for the same problem.
llvm-svn: 310159
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
index 9ef6a0e..b5b8aa3 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
@@ -640,16 +640,16 @@
unsigned AndZeros = AndRHS->getValue().logBase2();
// If types don't match we can still convert the select by introducing a zext
- // or a trunc of the 'and'. The trunc case requires that all of the truncated
- // bits are zero, we can figure that out by looking at the 'and' mask.
- if (AndZeros >= ValC.getBitWidth())
- return nullptr;
-
- Value *V = Builder.CreateZExtOrTrunc(LHS, SI.getType());
- if (ValZeros > AndZeros)
+ // or a trunc of the 'and'.
+ Value *V = LHS;
+ if (ValZeros > AndZeros) {
+ V = Builder.CreateZExtOrTrunc(V, SI.getType());
V = Builder.CreateShl(V, ValZeros - AndZeros);
- else if (ValZeros < AndZeros)
+ } else if (ValZeros < AndZeros) {
V = Builder.CreateLShr(V, AndZeros - ValZeros);
+ V = Builder.CreateZExtOrTrunc(V, SI.getType());
+ } else
+ V = Builder.CreateZExtOrTrunc(V, SI.getType());
// Okay, now we know that everything is set up, we just don't know whether we
// have a icmp_ne or icmp_eq and whether the true or false val is the zero.