Conservative fix for PR17827 - don't optimize a shift + and + compare sequence where the shift is logical unless the comparison is unsigned

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@196129 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 74 insertions, 0 deletions

diff --git a/test/Transforms/InstCombine/pr17827.ll b/test/Transforms/InstCombine/pr17827.ll
new file mode 100644
index 0000000000..a8b5926355
--- /dev/null
+++ b/test/Transforms/InstCombine/pr17827.ll
@@ -0,0 +1,74 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+; With left shift, the comparison should not be modified.
+; CHECK-LABEL: @test_shift_and_cmp_not_changed1(
+; CHECK: icmp slt i8 %andp, 32
+define i1 @test_shift_and_cmp_not_changed1(i8 %p) #0 {
+entry:
+  %shlp = shl i8 %p, 5
+  %andp = and i8 %shlp, -64
+  %cmp = icmp slt i8 %andp, 32
+  ret i1 %cmp
+}
+
+; With arithmetic right shift, the comparison should not be modified.
+; CHECK-LABEL: @test_shift_and_cmp_not_changed2(
+; CHECK: icmp slt i8 %andp, 32
+define i1 @test_shift_and_cmp_not_changed2(i8 %p) #0 {
+entry:
+  %shlp = ashr i8 %p, 5
+  %andp = and i8 %shlp, -64
+  %cmp = icmp slt i8 %andp, 32
+  ret i1 %cmp
+}
+
+; This should simplify functionally to the left shift case.
+; The extra input parameter should be optimized away.
+; CHECK-LABEL: @test_shift_and_cmp_changed1(
+; CHECK:  %andp = shl i8 %p, 5
+; CHECK-NEXT: %shl = and i8 %andp, -64
+; CHECK-NEXT:  %cmp = icmp slt i8 %shl, 32
+define i1 @test_shift_and_cmp_changed1(i8 %p, i8 %q) #0 {
+entry:
+  %andp = and i8 %p, 6
+  %andq = and i8 %q, 8
+  %or = or i8 %andq, %andp
+  %shl = shl i8 %or, 5
+  %ashr = ashr i8 %shl, 5
+  %cmp = icmp slt i8 %ashr, 1
+  ret i1 %cmp
+}
+
+; Unsigned compare allows a transformation to compare against 0.
+; CHECK-LABEL: @test_shift_and_cmp_changed2(
+; CHECK: icmp eq i8 %andp, 0
+define i1 @test_shift_and_cmp_changed2(i8 %p) #0 {
+entry:
+  %shlp = shl i8 %p, 5
+  %andp = and i8 %shlp, -64
+  %cmp = icmp ult i8 %andp, 32
+  ret i1 %cmp
+}
+
+; nsw on the shift should not affect the comparison.
+; CHECK-LABEL: @test_shift_and_cmp_changed3(
+; CHECK: icmp slt i8 %andp, 32
+define i1 @test_shift_and_cmp_changed3(i8 %p) #0 {
+entry:
+  %shlp = shl nsw i8 %p, 5
+  %andp = and i8 %shlp, -64
+  %cmp = icmp slt i8 %andp, 32
+  ret i1 %cmp
+}
+
+; Logical shift right allows a return true because the 'and' guarantees no bits are set.
+; CHECK-LABEL: @test_shift_and_cmp_changed4(
+; CHECK: ret i1 true
+define i1 @test_shift_and_cmp_changed4(i8 %p) #0 {
+entry:
+  %shlp = lshr i8 %p, 5
+  %andp = and i8 %shlp, -64
+  %cmp = icmp slt i8 %andp, 32
+  ret i1 %cmp
+}
+