Teach instcombine to look for booleans in wider integers when it encounters a

zext(icmp). It may be able to optimize that away. This fixes one of the cases
in PR5438.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@88830 91177308-0d34-0410-b5e6-96231b3b80d8

test/Transforms/InstCombine/compare-signs.ll

@@ -0,0 +1,28 @@
+; RUN: opt %S -instcombine -S | FileCheck %S
+; PR5438
+
+; TODO: This should also optimize down.
+;define i32 @bar(i32 %a, i32 %b) nounwind readnone {
+;entry:
+;        %0 = icmp sgt i32 %a, -1        ; <i1> [#uses=1]
+;        %1 = icmp slt i32 %b, 0         ; <i1> [#uses=1]
+;        %2 = xor i1 %1, %0              ; <i1> [#uses=1]
+;        %3 = zext i1 %2 to i32          ; <i32> [#uses=1]
+;        ret i32 %3
+;}
+
+define i32 @qaz(i32 %a, i32 %b) nounwind readnone {
+; CHECK: @qaz
+entry:
+; CHECK: xor i32 %a, %b
+; CHECK; lshr i32 %0, 31
+; CHECK: xor i32 %1, 1
+        %0 = lshr i32 %a, 31            ; <i32> [#uses=1]
+        %1 = lshr i32 %b, 31            ; <i32> [#uses=1]
+        %2 = icmp eq i32 %0, %1         ; <i1> [#uses=1]
+        %3 = zext i1 %2 to i32          ; <i32> [#uses=1]
+        ret i32 %3
+; CHECK-NOT: icmp
+; CHECK-NOT: zext
+; CHECK: ret i32 %2
+}