DAG: avoid duplicated truncating for sign extended operand

Summary:
When performing cmp for EQ/NE and the operand is sign extended, we can
avoid the truncaton if the bits to be tested are no less than origianl
bits.

Reviewers: eli.friedman

Subscribers: eli.friedman, aemerson, nemanjai, t.p.northover, llvm-commits

Differential Revision: https://reviews.llvm.org/D22933

llvm-svn: 277252

2 files changed, 112 insertions, 3 deletions

diff --git a/llvm/test/CodeGen/ARM/arm-shrink-wrapping.ll b/llvm/test/CodeGen/ARM/arm-shrink-wrapping.ll
index cb608fc18d9..93572b1e63d 100644
--- a/llvm/test/CodeGen/ARM/arm-shrink-wrapping.ll
+++ b/llvm/test/CodeGen/ARM/arm-shrink-wrapping.ll
@@ -501,9 +501,13 @@ declare i32 @someVariadicFunc(i32, ...)
 ;
 ; CHECK-LABEL: noreturn:
 ; DISABLE: push
-;
-; CHECK: tst{{(\.w)?}}  r0, #255
-; CHECK-NEXT: bne      [[ABORT:LBB[0-9_]+]]
+; ARM-ENABLE: cmp r0, #0
+; ARM-DISABLE: cmp r0, #0
+; ARM-ENABLE: bne [[ABORT:LBB[0-9_]+]]
+; ARM-DISABLE: bne [[ABORT:LBB[0-9_]+]]
+; THUMB-ENABLE: cbnz r0,  [[ABORT:LBB[0-9_]+]]
+; THUMB-DISABLE: cbnz r0,  [[ABORT:LBB[0-9_]+]]
+
 ;
 ; CHECK: mov{{s?}} r0, #42
 ;
diff --git a/llvm/test/CodeGen/ARM/no_redundant_trunc_for_cmp.ll b/llvm/test/CodeGen/ARM/no_redundant_trunc_for_cmp.ll
new file mode 100644
index 00000000000..7146c09ee80
--- /dev/null
+++ b/llvm/test/CodeGen/ARM/no_redundant_trunc_for_cmp.ll
@@ -0,0 +1,105 @@
+; This test check if redundant truncate for eq/ne cmp is skipped during code gen.
+;RUN: llc -mtriple=thumbv7-eabi < %s | FileCheck %s
+
+define void @test_zero(i16 signext %x) optsize {
+;CHECK-LABEL: test_zero
+entry:
+  %tobool = icmp eq i16 %x, 0
+  br i1 %tobool, label %if.else, label %if.then
+;CHECK-NOT: movw {{.*}}, #65535
+;CHECK: cbz r0,
+if.then:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @foo1 to void ()*)()
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @foo2 to void ()*)()
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  ret void
+}
+
+define void @test_i8_nonzero(i18 signext %x) optsize {
+;CHECK-LABEL: test_i8_nonzero
+entry:
+  %tobool = icmp eq i18 %x, 150
+  br i1 %tobool, label %if.else, label %if.then
+;CHECK-NOT: bfc
+;CHECK: cmp r{{[0-9]+}}, #150
+if.then:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @foo1 to void ()*)()
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @foo2 to void ()*)()
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  ret void
+}
+
+define void @test_i8_i16(i8 signext %x) optsize {
+;CHECK-LABEL: test_i8_i16
+entry:
+  %x16 = sext i8 %x to i16
+  %tobool = icmp eq i16 %x16, 300
+  br i1 %tobool, label %if.else, label %if.then
+;CHECK-NOT: uxth r0, r0
+;CHECK: cmp.w r0, #300
+if.then:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @foo1 to void ()*)()
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @foo2 to void ()*)()
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  ret void
+}
+
+define void @test_i16_i8(i16 signext %x) optsize {
+;CHECK-LABEL: test_i16_i8
+entry:
+;CHECK: uxtb [[REG:r[0-9+]]], r0
+;CHECK: cmp [[REG]], #128
+  %x8 = trunc i16 %x to i8
+  %tobool = icmp eq i8 %x8, 128
+  br i1 %tobool, label %if.else, label %if.then
+if.then:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @foo1 to void ()*)()
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @foo2 to void ()*)()
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  ret void
+}
+
+define void @test_zext_zero(i16 zeroext %x) optsize {
+;CHECK-LABEL: test_zext_zero
+entry:
+  %tobool = icmp eq i16 %x, 0
+  br i1 %tobool, label %if.else, label %if.then
+;CHECK-NOT: movw {{.*}}, #65535
+;CHECK: cbz r0,
+if.then:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @foo1 to void ()*)()
+  br label %if.end
+
+if.else:                                          ; preds = %entry
+  tail call void bitcast (void (...)* @foo2 to void ()*)()
+  br label %if.end
+
+if.end:                                           ; preds = %if.else, %if.then
+  ret void
+}
+
+
+declare void @foo1(...)
+declare void @foo2(...)
+
+