[NFC][DAGCombine][X86] '~(X - 1)' pattern tests

The fold 'A - (A & (B - 1))' -> 'A & (0 - B)'
added in 8dab0a4a7d691f2704f1079538e0ef29548db159
is too specific. It should just be 'A - (A & B)' -> 'A & (~B)',
but we currently fail to sink that '~' into `(B - 1)`.

Name: ~(X - 1)  ->  (0 - X)
%o = add i32 %X, -1
%r = xor i32 %o, -1
  =>
%r = sub i32 0, %X

https://rise4fun.com/Alive/rjU

diff --git a/llvm/test/CodeGen/X86/not-of-dec.ll b/llvm/test/CodeGen/X86/not-of-dec.ll
new file mode 100644 (file)
index 0000000..f3aece7
--- /dev/null
+++ b/llvm/test/CodeGen/X86/not-of-dec.ll
@@ -0,0 +1,120 @@
+; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
+; RUN: llc -mtriple=i686-unknown-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,X86
+; RUN: llc -mtriple=x86_64-unknown-linux-gnu < %s | FileCheck %s --check-prefixes=CHECK,X64
+
+; Fold
+;   ~(X - 1)
+; To
+;   - X
+;
+; This needs to be a backend-level fold because only by now pointers
+; are just registers; in middle-end IR this can only be done via @llvm.ptrmask()
+; intrinsic which is not sufficiently widely-spread yet.
+;
+; https://bugs.llvm.org/show_bug.cgi?id=44448
+
+; The basic positive tests
+
+define i32 @t0_32(i32 %alignment) nounwind {
+; X86-LABEL: t0_32:
+; X86:       # %bb.0:
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    decl %eax
+; X86-NEXT:    notl %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: t0_32:
+; X64:       # %bb.0:
+; X64-NEXT:    # kill: def $edi killed $edi def $rdi
+; X64-NEXT:    leal -1(%rdi), %eax
+; X64-NEXT:    notl %eax
+; X64-NEXT:    retq
+  %mask = add i32 %alignment, -1
+  %invmask = xor i32 %mask, -1
+  ret i32 %invmask
+}
+define i64 @t1_64(i64 %alignment) nounwind {
+; X86-LABEL: t1_64:
+; X86:       # %bb.0:
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %edx
+; X86-NEXT:    addl $-1, %eax
+; X86-NEXT:    adcl $-1, %edx
+; X86-NEXT:    notl %edx
+; X86-NEXT:    notl %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: t1_64:
+; X64:       # %bb.0:
+; X64-NEXT:    leaq -1(%rdi), %rax
+; X64-NEXT:    notq %rax
+; X64-NEXT:    retq
+  %mask = add i64 %alignment, -1
+  %invmask = xor i64 %mask, -1
+  ret i64 %invmask
+}
+
+; Extra use test
+
+define i32 @t2_extrause(i32 %alignment, i32* %mask_storage) nounwind {
+; X86-LABEL: t2_extrause:
+; X86:       # %bb.0:
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    decl %eax
+; X86-NEXT:    movl %eax, (%ecx)
+; X86-NEXT:    notl %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: t2_extrause:
+; X64:       # %bb.0:
+; X64-NEXT:    movl %edi, %eax
+; X64-NEXT:    decl %eax
+; X64-NEXT:    movl %eax, (%rsi)
+; X64-NEXT:    notl %eax
+; X64-NEXT:    retq
+  %mask = add i32 %alignment, -1
+  store i32 %mask, i32* %mask_storage
+  %invmask = xor i32 %mask, -1
+  ret i32 %invmask
+}
+
+; Negative tests
+
+define i32 @n3_not_dec(i32 %alignment) nounwind {
+; X86-LABEL: n3_not_dec:
+; X86:       # %bb.0:
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    incl %eax
+; X86-NEXT:    notl %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: n3_not_dec:
+; X64:       # %bb.0:
+; X64-NEXT:    # kill: def $edi killed $edi def $rdi
+; X64-NEXT:    leal 1(%rdi), %eax
+; X64-NEXT:    notl %eax
+; X64-NEXT:    retq
+  %mask = add i32 %alignment, 1 ; not -1
+  %invmask = xor i32 %mask, -1
+  ret i32 %invmask
+}
+
+define i32 @n4_not_not(i32 %alignment) nounwind {
+; X86-LABEL: n4_not_not:
+; X86:       # %bb.0:
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    decl %eax
+; X86-NEXT:    xorl $1, %eax
+; X86-NEXT:    retl
+;
+; X64-LABEL: n4_not_not:
+; X64:       # %bb.0:
+; X64-NEXT:    # kill: def $edi killed $edi def $rdi
+; X64-NEXT:    leal -1(%rdi), %eax
+; X64-NEXT:    xorl $1, %eax
+; X64-NEXT:    retq
+  %mask = add i32 %alignment, -1
+  %invmask = xor i32 %mask, 1 ; not -1
+  ret i32 %invmask
+}