[InstCombine] treat i1 as a special type in shouldChangeType()
This patch is based on the llvm-dev discussion here:
http://lists.llvm.org/pipermail/llvm-dev/2017-January/109631.html
Folding to i1 should always be desirable because that's better for value tracking
and we have special folds for i1 types.
I checked for other users of shouldChangeType() where this might have an effect,
but we already handle the i1 case differently than other types in all of those cases.
Side note: the default datalayout includes i1, so it seems we only find this gap in
shouldChangeType + phi folding for the case when there is (1) an explicit datalayout
without i1, (2) casting to i1 from a legal type, and (3) a phi with exactly 2 incoming
casted operands (as Björn mentioned).
Differential Revision: https://reviews.llvm.org/D29336
llvm-svn: 294066
diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 851569c..b74b3273 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -89,11 +89,13 @@
/// Return true if it is desirable to convert an integer computation from a
/// given bit width to a new bit width.
/// We don't want to convert from a legal to an illegal type or from a smaller
-/// to a larger illegal type.
+/// to a larger illegal type. A width of '1' is always treated as a legal type
+/// because i1 is a fundamental type in IR, and there are many specialized
+/// optimizations for i1 types.
bool InstCombiner::shouldChangeType(unsigned FromWidth,
unsigned ToWidth) const {
- bool FromLegal = DL.isLegalInteger(FromWidth);
- bool ToLegal = DL.isLegalInteger(ToWidth);
+ bool FromLegal = FromWidth == 1 || DL.isLegalInteger(FromWidth);
+ bool ToLegal = ToWidth == 1 || DL.isLegalInteger(ToWidth);
// If this is a legal integer from type, and the result would be an illegal
// type, don't do the transformation.
@@ -110,7 +112,9 @@
/// Return true if it is desirable to convert a computation from 'From' to 'To'.
/// We don't want to convert from a legal to an illegal type or from a smaller
-/// to a larger illegal type.
+/// to a larger illegal type. i1 is always treated as a legal type because it is
+/// a fundamental type in IR, and there are many specialized optimizations for
+/// i1 types.
bool InstCombiner::shouldChangeType(Type *From, Type *To) const {
assert(From->isIntegerTy() && To->isIntegerTy());