[X86/Atomics] (Semantically) revert G246098, switch back to the old atomic example

preames · preames · commit 027aa27d95c1 · 2019-11-05T11:24:27.000-08:00
When writing an email for a follow up proposal, I realized one of the diffs in the committed change was incorrect.  Digging into it revealed that the fix is complicated enough to require some thought, so reverting in the meantime.

The problem is visible in this diff (from the revert):
 ; X64-SSE-LABEL: store_fp128:
 ; X64-SSE:       # %bb.0:
-; X64-SSE-NEXT:    movaps %xmm0, (%rdi)
+; X64-SSE-NEXT:    subq $24, %rsp
+; X64-SSE-NEXT:    .cfi_def_cfa_offset 32
+; X64-SSE-NEXT:    movaps %xmm0, (%rsp)
+; X64-SSE-NEXT:    movq (%rsp), %rsi
+; X64-SSE-NEXT:    movq {{[0-9]+}}(%rsp), %rdx
+; X64-SSE-NEXT:    callq __sync_lock_test_and_set_16
+; X64-SSE-NEXT:    addq $24, %rsp
+; X64-SSE-NEXT:    .cfi_def_cfa_offset 8
 ; X64-SSE-NEXT:    retq
   store atomic fp128 %v, fp128* %fptr unordered, align 16
   ret void

The problem here is three fold:
1) x86-64 doesn't guarantee atomicity of anything larger than 8 bytes.  Some platforms observably break this guarantee, others don't, but the codegen isn't considering this, so it's wrong on at least some platforms.
2) When I started to track down the problem, I discovered that DAGCombiner had stripped the atomicity off the store entirely.  This comes down to idiomatic usage of DAG.getStore passing all MMO components separately as opposed to just passing the MMO.
3) On x86 (not -64), there are cases where 8 byte atomiciy is supported, but only for floating point operations.  This would seem to imply that operation typing matters for correctness, and DAGCombine happily folds away bitcasts.  I'm not 100% sure there's a problem here, but I'm not entirely sure there isn't either.

I plan on returning to each issue in turn;  sorry for the churn here.
diff --git a/llvm/lib/Target/X86/X86ISelLowering.cpp b/llvm/lib/Target/X86/X86ISelLowering.cpp
@@ -87,7 +87,7 @@ static cl::opt<bool> MulConstantOptimization(
     cl::Hidden);
 
 static cl::opt<bool> ExperimentalUnorderedISEL(
-    "x86-experimental-unordered-atomic-isel", cl::init(true),
+    "x86-experimental-unordered-atomic-isel", cl::init(false),
     cl::desc("Use LoadSDNode and StoreSDNode instead of "
              "AtomicSDNode for unordered atomic loads and "
              "stores respectively."),
diff --git a/llvm/test/CodeGen/X86/atomic-non-integer-fp128.ll b/llvm/test/CodeGen/X86/atomic-non-integer-fp128.ll
@@ -21,7 +21,14 @@ define void @store_fp128(fp128* %fptr, fp128 %v) {
 ;
 ; X64-SSE-LABEL: store_fp128:
 ; X64-SSE:       # %bb.0:
-; X64-SSE-NEXT:    movaps %xmm0, (%rdi)
+; X64-SSE-NEXT:    subq $24, %rsp
+; X64-SSE-NEXT:    .cfi_def_cfa_offset 32
+; X64-SSE-NEXT:    movaps %xmm0, (%rsp)
+; X64-SSE-NEXT:    movq (%rsp), %rsi
+; X64-SSE-NEXT:    movq {{[0-9]+}}(%rsp), %rdx
+; X64-SSE-NEXT:    callq __sync_lock_test_and_set_16
+; X64-SSE-NEXT:    addq $24, %rsp
+; X64-SSE-NEXT:    .cfi_def_cfa_offset 8
 ; X64-SSE-NEXT:    retq
   store atomic fp128 %v, fp128* %fptr unordered, align 16
   ret void
diff --git a/llvm/test/CodeGen/X86/atomic-non-integer.ll b/llvm/test/CodeGen/X86/atomic-non-integer.ll
@@ -114,26 +114,12 @@ define void @store_half(half* %fptr, half %v) {
 }
 
 define void @store_float(float* %fptr, float %v) {
-; X86-SSE-LABEL: store_float:
-; X86-SSE:       # %bb.0:
-; X86-SSE-NEXT:    movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
-; X86-SSE-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-SSE-NEXT:    movss %xmm0, (%eax)
-; X86-SSE-NEXT:    retl
-;
-; X86-AVX-LABEL: store_float:
-; X86-AVX:       # %bb.0:
-; X86-AVX-NEXT:    vmovss {{.*#+}} xmm0 = mem[0],zero,zero,zero
-; X86-AVX-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-AVX-NEXT:    vmovss %xmm0, (%eax)
-; X86-AVX-NEXT:    retl
-;
-; X86-NOSSE-LABEL: store_float:
-; X86-NOSSE:       # %bb.0:
-; X86-NOSSE-NEXT:    flds {{[0-9]+}}(%esp)
-; X86-NOSSE-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-NOSSE-NEXT:    fstps (%eax)
-; X86-NOSSE-NEXT:    retl
+; X86-LABEL: store_float:
+; X86:       # %bb.0:
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; X86-NEXT:    movl %ecx, (%eax)
+; X86-NEXT:    retl
 ;
 ; X64-SSE-LABEL: store_float:
 ; X64-SSE:       # %bb.0:
@@ -176,16 +162,16 @@ define void @store_double(double* %fptr, double %v) {
 ;
 ; X86-SSE2-LABEL: store_double:
 ; X86-SSE2:       # %bb.0:
-; X86-SSE2-NEXT:    movsd {{.*#+}} xmm0 = mem[0],zero
 ; X86-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-SSE2-NEXT:    movsd %xmm0, (%eax)
+; X86-SSE2-NEXT:    movsd {{.*#+}} xmm0 = mem[0],zero
+; X86-SSE2-NEXT:    movlps %xmm0, (%eax)
 ; X86-SSE2-NEXT:    retl
 ;
 ; X86-AVX-LABEL: store_double:
 ; X86-AVX:       # %bb.0:
-; X86-AVX-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
 ; X86-AVX-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-AVX-NEXT:    vmovsd %xmm0, (%eax)
+; X86-AVX-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
+; X86-AVX-NEXT:    vmovlps %xmm0, (%eax)
 ; X86-AVX-NEXT:    retl
 ;
 ; X86-NOSSE-LABEL: store_double:
@@ -290,12 +276,26 @@ define void @store_fp128(fp128* %fptr, fp128 %v) {
 ;
 ; X64-SSE-LABEL: store_fp128:
 ; X64-SSE:       # %bb.0:
-; X64-SSE-NEXT:    movaps %xmm0, (%rdi)
+; X64-SSE-NEXT:    subq $24, %rsp
+; X64-SSE-NEXT:    .cfi_def_cfa_offset 32
+; X64-SSE-NEXT:    movaps %xmm0, (%rsp)
+; X64-SSE-NEXT:    movq (%rsp), %rsi
+; X64-SSE-NEXT:    movq {{[0-9]+}}(%rsp), %rdx
+; X64-SSE-NEXT:    callq __sync_lock_test_and_set_16
+; X64-SSE-NEXT:    addq $24, %rsp
+; X64-SSE-NEXT:    .cfi_def_cfa_offset 8
 ; X64-SSE-NEXT:    retq
 ;
 ; X64-AVX-LABEL: store_fp128:
 ; X64-AVX:       # %bb.0:
-; X64-AVX-NEXT:    vmovaps %xmm0, (%rdi)
+; X64-AVX-NEXT:    subq $24, %rsp
+; X64-AVX-NEXT:    .cfi_def_cfa_offset 32
+; X64-AVX-NEXT:    vmovaps %xmm0, (%rsp)
+; X64-AVX-NEXT:    movq (%rsp), %rsi
+; X64-AVX-NEXT:    movq {{[0-9]+}}(%rsp), %rdx
+; X64-AVX-NEXT:    callq __sync_lock_test_and_set_16
+; X64-AVX-NEXT:    addq $24, %rsp
+; X64-AVX-NEXT:    .cfi_def_cfa_offset 8
 ; X64-AVX-NEXT:    retq
   store atomic fp128 %v, fp128* %fptr unordered, align 16
   ret void
@@ -383,11 +383,53 @@ define half @load_half(half* %fptr) {
 }
 
 define float @load_float(float* %fptr) {
-; X86-LABEL: load_float:
-; X86:       # %bb.0:
-; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-NEXT:    flds (%eax)
-; X86-NEXT:    retl
+; X86-SSE1-LABEL: load_float:
+; X86-SSE1:       # %bb.0:
+; X86-SSE1-NEXT:    pushl %eax
+; X86-SSE1-NEXT:    .cfi_def_cfa_offset 8
+; X86-SSE1-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-SSE1-NEXT:    movl (%eax), %eax
+; X86-SSE1-NEXT:    movl %eax, (%esp)
+; X86-SSE1-NEXT:    flds (%esp)
+; X86-SSE1-NEXT:    popl %eax
+; X86-SSE1-NEXT:    .cfi_def_cfa_offset 4
+; X86-SSE1-NEXT:    retl
+;
+; X86-SSE2-LABEL: load_float:
+; X86-SSE2:       # %bb.0:
+; X86-SSE2-NEXT:    pushl %eax
+; X86-SSE2-NEXT:    .cfi_def_cfa_offset 8
+; X86-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-SSE2-NEXT:    movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
+; X86-SSE2-NEXT:    movss %xmm0, (%esp)
+; X86-SSE2-NEXT:    flds (%esp)
+; X86-SSE2-NEXT:    popl %eax
+; X86-SSE2-NEXT:    .cfi_def_cfa_offset 4
+; X86-SSE2-NEXT:    retl
+;
+; X86-AVX-LABEL: load_float:
+; X86-AVX:       # %bb.0:
+; X86-AVX-NEXT:    pushl %eax
+; X86-AVX-NEXT:    .cfi_def_cfa_offset 8
+; X86-AVX-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-AVX-NEXT:    vmovss {{.*#+}} xmm0 = mem[0],zero,zero,zero
+; X86-AVX-NEXT:    vmovss %xmm0, (%esp)
+; X86-AVX-NEXT:    flds (%esp)
+; X86-AVX-NEXT:    popl %eax
+; X86-AVX-NEXT:    .cfi_def_cfa_offset 4
+; X86-AVX-NEXT:    retl
+;
+; X86-NOSSE-LABEL: load_float:
+; X86-NOSSE:       # %bb.0:
+; X86-NOSSE-NEXT:    pushl %eax
+; X86-NOSSE-NEXT:    .cfi_def_cfa_offset 8
+; X86-NOSSE-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NOSSE-NEXT:    movl (%eax), %eax
+; X86-NOSSE-NEXT:    movl %eax, (%esp)
+; X86-NOSSE-NEXT:    flds (%esp)
+; X86-NOSSE-NEXT:    popl %eax
+; X86-NOSSE-NEXT:    .cfi_def_cfa_offset 4
+; X86-NOSSE-NEXT:    retl
 ;
 ; X64-SSE-LABEL: load_float:
 ; X64-SSE:       # %bb.0:
@@ -403,11 +445,61 @@ define float @load_float(float* %fptr) {
 }
 
 define double @load_double(double* %fptr) {
-; X86-LABEL: load_double:
-; X86:       # %bb.0:
-; X86-NEXT:    movl {{[0-9]+}}(%esp), %eax
-; X86-NEXT:    fldl (%eax)
-; X86-NEXT:    retl
+; X86-SSE1-LABEL: load_double:
+; X86-SSE1:       # %bb.0:
+; X86-SSE1-NEXT:    subl $20, %esp
+; X86-SSE1-NEXT:    .cfi_def_cfa_offset 24
+; X86-SSE1-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-SSE1-NEXT:    fildll (%eax)
+; X86-SSE1-NEXT:    fistpll {{[0-9]+}}(%esp)
+; X86-SSE1-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-SSE1-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; X86-SSE1-NEXT:    movl %ecx, {{[0-9]+}}(%esp)
+; X86-SSE1-NEXT:    movl %eax, (%esp)
+; X86-SSE1-NEXT:    fldl (%esp)
+; X86-SSE1-NEXT:    addl $20, %esp
+; X86-SSE1-NEXT:    .cfi_def_cfa_offset 4
+; X86-SSE1-NEXT:    retl
+;
+; X86-SSE2-LABEL: load_double:
+; X86-SSE2:       # %bb.0:
+; X86-SSE2-NEXT:    subl $12, %esp
+; X86-SSE2-NEXT:    .cfi_def_cfa_offset 16
+; X86-SSE2-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-SSE2-NEXT:    movsd {{.*#+}} xmm0 = mem[0],zero
+; X86-SSE2-NEXT:    movlps %xmm0, (%esp)
+; X86-SSE2-NEXT:    fldl (%esp)
+; X86-SSE2-NEXT:    addl $12, %esp
+; X86-SSE2-NEXT:    .cfi_def_cfa_offset 4
+; X86-SSE2-NEXT:    retl
+;
+; X86-AVX-LABEL: load_double:
+; X86-AVX:       # %bb.0:
+; X86-AVX-NEXT:    subl $12, %esp
+; X86-AVX-NEXT:    .cfi_def_cfa_offset 16
+; X86-AVX-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-AVX-NEXT:    vmovsd {{.*#+}} xmm0 = mem[0],zero
+; X86-AVX-NEXT:    vmovlps %xmm0, (%esp)
+; X86-AVX-NEXT:    fldl (%esp)
+; X86-AVX-NEXT:    addl $12, %esp
+; X86-AVX-NEXT:    .cfi_def_cfa_offset 4
+; X86-AVX-NEXT:    retl
+;
+; X86-NOSSE-LABEL: load_double:
+; X86-NOSSE:       # %bb.0:
+; X86-NOSSE-NEXT:    subl $20, %esp
+; X86-NOSSE-NEXT:    .cfi_def_cfa_offset 24
+; X86-NOSSE-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NOSSE-NEXT:    fildll (%eax)
+; X86-NOSSE-NEXT:    fistpll {{[0-9]+}}(%esp)
+; X86-NOSSE-NEXT:    movl {{[0-9]+}}(%esp), %eax
+; X86-NOSSE-NEXT:    movl {{[0-9]+}}(%esp), %ecx
+; X86-NOSSE-NEXT:    movl %ecx, {{[0-9]+}}(%esp)
+; X86-NOSSE-NEXT:    movl %eax, (%esp)
+; X86-NOSSE-NEXT:    fldl (%esp)
+; X86-NOSSE-NEXT:    addl $20, %esp
+; X86-NOSSE-NEXT:    .cfi_def_cfa_offset 4
+; X86-NOSSE-NEXT:    retl
 ;
 ; X64-SSE-LABEL: load_double:
 ; X64-SSE:       # %bb.0:
@@ -465,10 +557,10 @@ define fp128 @load_fp128(fp128* %fptr) {
 ; X86-SSE-NEXT:    movl {{[0-9]+}}(%esp), %ecx
 ; X86-SSE-NEXT:    movl {{[0-9]+}}(%esp), %edx
 ; X86-SSE-NEXT:    movl {{[0-9]+}}(%esp), %edi
-; X86-SSE-NEXT:    movl %edi, 12(%esi)
-; X86-SSE-NEXT:    movl %edx, 8(%esi)
-; X86-SSE-NEXT:    movl %ecx, 4(%esi)
+; X86-SSE-NEXT:    movl %edi, 8(%esi)
+; X86-SSE-NEXT:    movl %edx, 12(%esi)
 ; X86-SSE-NEXT:    movl %eax, (%esi)
+; X86-SSE-NEXT:    movl %ecx, 4(%esi)
 ; X86-SSE-NEXT:    movl %esi, %eax
 ; X86-SSE-NEXT:    addl $20, %esp
 ; X86-SSE-NEXT:    .cfi_def_cfa_offset 12
@@ -546,10 +638,10 @@ define fp128 @load_fp128(fp128* %fptr) {
 ; X86-NOSSE-NEXT:    movl {{[0-9]+}}(%esp), %ecx
 ; X86-NOSSE-NEXT:    movl {{[0-9]+}}(%esp), %edx
 ; X86-NOSSE-NEXT:    movl {{[0-9]+}}(%esp), %edi
-; X86-NOSSE-NEXT:    movl %edi, 12(%esi)
-; X86-NOSSE-NEXT:    movl %edx, 8(%esi)
-; X86-NOSSE-NEXT:    movl %ecx, 4(%esi)
+; X86-NOSSE-NEXT:    movl %edi, 8(%esi)
+; X86-NOSSE-NEXT:    movl %edx, 12(%esi)
 ; X86-NOSSE-NEXT:    movl %eax, (%esi)
+; X86-NOSSE-NEXT:    movl %ecx, 4(%esi)
 ; X86-NOSSE-NEXT:    movl %esi, %eax
 ; X86-NOSSE-NEXT:    addl $20, %esp
 ; X86-NOSSE-NEXT:    .cfi_def_cfa_offset 12
@@ -561,12 +653,34 @@ define fp128 @load_fp128(fp128* %fptr) {
 ;
 ; X64-SSE-LABEL: load_fp128:
 ; X64-SSE:       # %bb.0:
-; X64-SSE-NEXT:    movaps (%rdi), %xmm0
+; X64-SSE-NEXT:    subq $24, %rsp
+; X64-SSE-NEXT:    .cfi_def_cfa_offset 32
+; X64-SSE-NEXT:    xorl %esi, %esi
+; X64-SSE-NEXT:    xorl %edx, %edx
+; X64-SSE-NEXT:    xorl %ecx, %ecx
+; X64-SSE-NEXT:    xorl %r8d, %r8d
+; X64-SSE-NEXT:    callq __sync_val_compare_and_swap_16
+; X64-SSE-NEXT:    movq %rdx, {{[0-9]+}}(%rsp)
+; X64-SSE-NEXT:    movq %rax, (%rsp)
+; X64-SSE-NEXT:    movaps (%rsp), %xmm0
+; X64-SSE-NEXT:    addq $24, %rsp
+; X64-SSE-NEXT:    .cfi_def_cfa_offset 8
 ; X64-SSE-NEXT:    retq
 ;
 ; X64-AVX-LABEL: load_fp128:
 ; X64-AVX:       # %bb.0:
-; X64-AVX-NEXT:    vmovaps (%rdi), %xmm0
+; X64-AVX-NEXT:    subq $24, %rsp
+; X64-AVX-NEXT:    .cfi_def_cfa_offset 32
+; X64-AVX-NEXT:    xorl %esi, %esi
+; X64-AVX-NEXT:    xorl %edx, %edx
+; X64-AVX-NEXT:    xorl %ecx, %ecx
+; X64-AVX-NEXT:    xorl %r8d, %r8d
+; X64-AVX-NEXT:    callq __sync_val_compare_and_swap_16
+; X64-AVX-NEXT:    movq %rdx, {{[0-9]+}}(%rsp)
+; X64-AVX-NEXT:    movq %rax, (%rsp)
+; X64-AVX-NEXT:    vmovaps (%rsp), %xmm0
+; X64-AVX-NEXT:    addq $24, %rsp
+; X64-AVX-NEXT:    .cfi_def_cfa_offset 8
 ; X64-AVX-NEXT:    retq
   %v = load atomic fp128, fp128* %fptr unordered, align 16
   ret fp128 %v
diff --git a/llvm/test/CodeGen/X86/combineIncDecVector-crash.ll b/llvm/test/CodeGen/X86/combineIncDecVector-crash.ll
@@ -19,11 +19,11 @@ define void @TestvMeth(i32 %0, i64 %1) gc "statepoint-example" !prof !1 {
 ; CHECK-NEXT:    callq newarray
 ; CHECK-NEXT:  .Ltmp0:
 ; CHECK-NEXT:    movss {{.*#+}} xmm0 = mem[0],zero,zero,zero
+; CHECK-NEXT:    addss (%rax), %xmm0
 ; CHECK-NEXT:    movdqu (%rax), %xmm1
 ; CHECK-NEXT:    pcmpeqd %xmm2, %xmm2
 ; CHECK-NEXT:    psubd %xmm2, %xmm1
 ; CHECK-NEXT:    movdqu %xmm1, (%rax)
-; CHECK-NEXT:    addss {{.*}}(%rip), %xmm0
 ; CHECK-NEXT:    movss %xmm0, (%rax)
 bci_0:
    %token418 = call token (i64, i32, i8 * (i64, i32, i32, i32)*, i32,
