[llvm-branch-commits] [compiler-rt] [compiler-rt][ARM] Optimized single-precision FP comparisons (PR #179925)

[Simon Tatham via llvm-branch-commits]

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@@ -0,0 +1,55 @@
+//===-- cmpsf2.S - single-precision floating point comparison -------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+//
+// This function has the semantics of GNU __cmpsf2: it's a three-way compare
+// which returns <0 if x<y, 0 if x==y, and >0 if x>y. If the result is
+// unordered (i.e. x or y or both is NaN) then it returns >0.
+//
+// This also makes it suitable for use as all of __eqsf2, __nesf2, __ltsf2 or
+// __lesf2.
+//
+//===----------------------------------------------------------------------===//
+
+#include "../../assembly.h"
+
+  .syntax unified
+  .text
+  .p2align 2
+
+op0 .req r0
+op1 .req r1
+.macro SetReturnRegister
+  bhi 0f
+  blo 1f
+  movs r0, #0
+  bx lr
+0:
+  movs r0, #1
+  bx lr
+1:
+  movs r0, #1
+  rsbs r0, r0, #0
+  bx lr
+.endm
+
+DEFINE_COMPILERRT_FUNCTION_ALIAS(__cmpsf2, __compiler_rt_softfp_cmpsf2)
+DEFINE_COMPILERRT_FUNCTION_ALIAS(__lesf2, __cmpsf2)
+DEFINE_COMPILERRT_FUNCTION_ALIAS(__ltsf2, __cmpsf2)
+DEFINE_COMPILERRT_FUNCTION_ALIAS(__eqsf2, __cmpsf2)
+DEFINE_COMPILERRT_FUNCTION_ALIAS(__nesf2, __cmpsf2)
+
+DEFINE_COMPILERRT_THUMB_FUNCTION(__compiler_rt_softfp_cmpsf2)
+  #include "fcmp.h"
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statham-arm wrote:

I admit I hadn't thought of `.include` (or even known it existed). But I don't think it would work correctly in this case, because inside `fcmp.h` I'm using macros defined via `#define`, particularly `LOCAL_LABEL` from the general compiler-rt assembly headers. If you use `.include`, then it's processed by the actual assembler after cpp has completely finished running, so it's too late for cpp macros in the included file to be expanded.

Also, it would introduce a build-system bug, because the `-MD` dependency tracking only accounts for files included by the preprocessor. So the make/ninja/whatever layer wouldn't know that modifying `fcmp.S` meant `cmpsf2.o` needed rebuilding.

https://github.com/llvm/llvm-project/pull/179925