[AArch64][test] Improve pr166870.ll test case

[asb]

As pointed out in post-commit discussion on #167336 #167336 (comment), although the test case succeeds in showing a codegen difference now the faulty MachineCopyPropagation logic was removed, the example was reduced so much that it actually would have been legal to remove the seemingly redundant mov.

This is a re-reduction of that test case which should now demonstrate a mov that can't safely be removed (mov w9, w9) because the upper bits no longer being zeroed may alter the program logic.

[llvmbot]

@llvm/pr-subscribers-backend-aarch64

Author: Alex Bradbury (asb)

Changes

As pointed out in post-commit discussion on #167336 <#167336 (comment)>, although the test case succeeds in showing a codegen difference now the faulty MachineCopyPropagation logic was removed, the example was reduced so much that it actually would have been legal to remove the seemingly redundant mov.

This is a re-reduction of that test case which should now demonstrate a mov that can't safely be removed (mov w9, w9) because the upper bits no longer being zeroed may alter the program logic.

---

Full diff: https://github.com/llvm/llvm-project/pull/168194.diff

1 Files Affected:

• (modified) llvm/test/CodeGen/AArch64/pr166870.ll (+77-46)

diff --git a/llvm/test/CodeGen/AArch64/pr166870.ll b/llvm/test/CodeGen/AArch64/pr166870.ll
index dc23f51987635..d6f99c67a01ff 100644
--- a/llvm/test/CodeGen/AArch64/pr166870.ll
+++ b/llvm/test/CodeGen/AArch64/pr166870.ll
@@ -1,68 +1,99 @@
 ; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py UTC_ARGS: --version 6
 ; RUN: llc -O3 < %s -mtriple=aarch64 | FileCheck %s
 
-; The seemingly redundant mov where src_reg == dst_reg shouldn't be removed,
-; because it has the effect of zeroing the upper bits in x8.
+; The seemingly redundant wreg mov where src_reg == dst_reg shouldn't be
+; removed, because it has the effect of zeroing the upper bits in the matching
+; xreg.
 
-define i32 @ham(i32 %arg, i1 %arg1, i1 %arg2, ptr %arg3) nounwind {
-; CHECK-LABEL: ham:
+define i32 @widget(i32 %arg, i32 %arg1, i1 %arg2, ptr %arg3, i1 %arg4) #0 nounwind {
+; CHECK-LABEL: widget:
 ; CHECK:       // %bb.0: // %bb
-; CHECK-NEXT:    stp x30, x21, [sp, #-32]! // 16-byte Folded Spill
-; CHECK-NEXT:    stp x20, x19, [sp, #16] // 16-byte Folded Spill
-; CHECK-NEXT:    tbnz w1, #0, .LBB0_3
-; CHECK-NEXT:  // %bb.1: // %bb4
-; CHECK-NEXT:    tbnz w2, #0, .LBB0_3
-; CHECK-NEXT:  // %bb.2: // %bb5
-; CHECK-NEXT:    mov x19, x3
-; CHECK-NEXT:    mov w21, w1
-; CHECK-NEXT:    mov w20, w0
-; CHECK-NEXT:    bl zot
-; CHECK-NEXT:    tbz w21, #0, .LBB0_4
-; CHECK-NEXT:  .LBB0_3: // %bb6
-; CHECK-NEXT:    ldp x20, x19, [sp, #16] // 16-byte Folded Reload
-; CHECK-NEXT:    mov w0, wzr
-; CHECK-NEXT:    ldp x30, x21, [sp], #32 // 16-byte Folded Reload
+; CHECK-NEXT:    tbz w2, #0, .LBB0_2
+; CHECK-NEXT:  // %bb.1:
+; CHECK-NEXT:    mov w0, #1 // =0x1
+; CHECK-NEXT:    ret
+; CHECK-NEXT:  .LBB0_2: // %bb5
+; CHECK-NEXT:    tbz w4, #0, .LBB0_4
+; CHECK-NEXT:  // %bb.3:
+; CHECK-NEXT:    mov w0, #0 // =0x0
 ; CHECK-NEXT:    ret
-; CHECK-NEXT:  .LBB0_4:
-; CHECK-NEXT:    mov w8, w20
-; CHECK-NEXT:    mov w20, wzr
+; CHECK-NEXT:  .LBB0_4: // %bb6
+; CHECK-NEXT:    str x30, [sp, #-48]! // 8-byte Folded Spill
+; CHECK-NEXT:    stp x22, x21, [sp, #16] // 16-byte Folded Spill
+; CHECK-NEXT:    stp x20, x19, [sp, #32] // 16-byte Folded Spill
+; CHECK-NEXT:    mov x19, x3
+; CHECK-NEXT:    mov x20, x0
+; CHECK-NEXT:    mov x21, x1
+; CHECK-NEXT:    bl baz
+; CHECK-NEXT:    mov w0, #0 // =0x0
+; CHECK-NEXT:    cbnz wzr, .LBB0_11
+; CHECK-NEXT:  // %bb.5: // %bb6
+; CHECK-NEXT:    mov w10, #1 // =0x1
+; CHECK-NEXT:    cbnz w10, .LBB0_11
+; CHECK-NEXT:  // %bb.6: // %bb7
+; CHECK-NEXT:    cbnz w10, .LBB0_10
+; CHECK-NEXT:  // %bb.7: // %bb8
+; CHECK-NEXT:    mov x8, x21
+; CHECK-NEXT:    mov x9, x20
+; CHECK-NEXT:    mov w20, #0 // =0x0
+; CHECK-NEXT:    mov w9, w9
+; CHECK-NEXT:    mov x21, x9
 ; CHECK-NEXT:    mov w8, w8
-; CHECK-NEXT:    mov w21, w8
-; CHECK-NEXT:  .LBB0_5: // %bb7
+; CHECK-NEXT:    mov x22, x8
+; CHECK-NEXT:  .LBB0_8: // %bb10
 ; CHECK-NEXT:    // =>This Inner Loop Header: Depth=1
 ; CHECK-NEXT:    strb w20, [x19]
-; CHECK-NEXT:    cbnz x21, .LBB0_5
-; CHECK-NEXT:  // %bb.6: // %bb8
-; CHECK-NEXT:    // in Loop: Header=BB0_5 Depth=1
-; CHECK-NEXT:    bl quux
-; CHECK-NEXT:    b .LBB0_5
+; CHECK-NEXT:    cbnz x21, .LBB0_8
+; CHECK-NEXT:  // %bb.9: // %bb12
+; CHECK-NEXT:    // in Loop: Header=BB0_8 Depth=1
+; CHECK-NEXT:    bl snork
+; CHECK-NEXT:    cbnz x22, .LBB0_8
+; CHECK-NEXT:  .LBB0_10:
+; CHECK-NEXT:    mov w0, #0 // =0x0
+; CHECK-NEXT:  .LBB0_11:
+; CHECK-NEXT:    ldp x20, x19, [sp, #32] // 16-byte Folded Reload
+; CHECK-NEXT:    ldp x22, x21, [sp, #16] // 16-byte Folded Reload
+; CHECK-NEXT:    ldr x30, [sp], #48 // 8-byte Folded Reload
+; CHECK-NEXT:    ret
 bb:
-  br i1 %arg1, label %bb6, label %bb4
-
-bb4:
-  %load = load ptr, ptr null, align 8
-  br i1 %arg2, label %bb6, label %bb5
+  br i1 %arg2, label %bb14, label %bb5
 
 bb5:
-  %call = call i32 @zot() #0
-  %zext = zext i32 %arg to i64
-  br i1 %arg1, label %bb6, label %bb7
+  %load = load ptr, ptr null, align 8
+  br i1 %arg4, label %bb14, label %bb6
 
 bb6:
-  ret i32 0
+  %call = call i32 @baz() #1
+  %or = or i1 false, true
+  br i1 %or, label %bb14, label %bb7
 
 bb7:
-  store i8 0, ptr %arg3, align 1
-  %icmp = icmp eq i64 %zext, 0
-  br i1 %icmp, label %bb8, label %bb7
+  %icmp = icmp eq i32 0, 0
+  %zext = zext i32 %arg to i64
+  br i1 %icmp, label %bb14, label %bb8
 
 bb8:
-  call void @quux()
-  br label %bb7
+  %zext9 = zext i32 %arg1 to i64
+  br label %bb10
+
+bb10:
+  store i8 0, ptr %arg3, align 1
+  %icmp11 = icmp eq i64 %zext, 0
+  br i1 %icmp11, label %bb12, label %bb10
+
+bb12:
+  call void @snork()
+  %icmp13 = icmp eq i64 0, %zext9
+  br i1 %icmp13, label %bb14, label %bb10
+
+bb14:
+  %phi = phi i32 [ 0, %bb6 ], [ 0, %bb7 ], [ 0, %bb12 ], [ 1, %bb ], [ 0, %bb5 ]
+  ret i32 %phi
 }
 
-declare i32 @zot()
+declare i32 @baz()
 
-declare void @quux()
+declare void @snork()
 
-attributes #0 = { returns_twice }
+attributes #0 = { "target-cpu"="apple-m1" }
+attributes #1 = { returns_twice }

[davemgreen]

Thanks for doing this - LGTM. You even managed to find two examples of it going wrong.

(I think the reason we see it being incorrect here and not in other cases it due to mcpu=apple using +zcm-gpr64 but not +zcm-gpr32, so the grp32 COPYs prefer to get lowered to a mov x, not a mov w as we would usually use. It means the top bits are not cleared by other movs).