[PowerPC] Handle cmp op promotion for SELECT[_CC] nodes in PPCTL::DAGCombineExtBoolTrunc
PPCTargetLowering::DAGCombineExtBoolTrunc contains logic to remove unwanted
truncations and extensions when dealing with nodes of the form:
zext(binary-ops(binary-ops(trunc(x), trunc(y)), ...)
There was a FIXME in the implementation (now removed) regarding the fact that
the function would abort the transformations if any of the non-output operands
of a SELECT or SELECT_CC node would need to be promoted (because they were
also output operands, for example). As a result, we continued to generate
unnecessary zero-extends for code such as this:
unsigned foo(unsigned a, unsigned b) {
return (a <= b) ? a : b;
}
which would produce:
cmplw 0, 3, 4
isel 3, 4, 3, 1
rldicl 3, 3, 0, 32
blr
and now we produce:
cmplw 0, 3, 4
isel 3, 4, 3, 1
blr
which is better in the obvious way.
llvm-svn: 224213
diff --git a/llvm/test/CodeGen/PowerPC/rm-zext.ll b/llvm/test/CodeGen/PowerPC/rm-zext.ll
index 1e60d11..8fab38a 100644
--- a/llvm/test/CodeGen/PowerPC/rm-zext.ll
+++ b/llvm/test/CodeGen/PowerPC/rm-zext.ll
@@ -28,5 +28,16 @@
; CHECK: blr
}
+define zeroext i32 @min(i32 zeroext %a, i32 zeroext %b) #0 {
+entry:
+ %cmp = icmp ule i32 %a, %b
+ %cond = select i1 %cmp, i32 %a, i32 %b
+ ret i32 %cond
+
+; CHECK-LABEL @min
+; CHECK-NOT: rldicl 3, {{[0-9]+}}, 0, 32
+; CHECK: blr
+}
+
attributes #0 = { nounwind readnone }