[llvm] [clang] [llvm][ARM] Emit MVE .arch_extension after .fpu directive if it does not include MVE features (PR #71545)

[David Spickett via llvm-commits]

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@@ -0,0 +1,56 @@
+; REQUIRES: arm-registered-target
+; RUN: %clang --target=arm-none-eabi -mcpu=cortex-m85 -mfloat-abi=hard -save-temps=obj -S -o - %s | FileCheck %s
+; RUN: %clang --target=arm-none-eabi -mcpu=cortex-m55 -mfloat-abi=hard -save-temps=obj -S -o - %s | FileCheck %s
+; RUN: %clang --target=arm-none-eabi -mcpu=cortex-m85 -mfloat-abi=hard -O2 -c -mthumb -save-temps=obj %s
+; RUN: %clang --target=arm-none-eabi -mcpu=cortex-m55 -mfloat-abi=hard -O2 -c -mthumb -save-temps=obj %s
+; CHECK: .fpu   fpv5-d16
+; CHECK  .arch_extension mve.fp
+target datalayout = "e-m:e-p:32:32-Fi8-i64:64-v128:64:128-a:0:32-n32-S64"
+target triple = "thumbv8.1m.main-none-unknown-eabihf"
+
+%struct.dummy_t = type { float, float, float, float }
+
+define dso_local signext i8 @foo(ptr noundef %handle) #0 {
+entry:
+  %handle.addr = alloca ptr, align 4
+  store ptr %handle, ptr %handle.addr, align 4
+  %0 = load ptr, ptr %handle.addr, align 4
+  %a = getelementptr inbounds %struct.dummy_t, ptr %0, i32 0, i32 0
+  %1 = load float, ptr %a, align 4
+  %sub = fsub float 0x3F5439DE40000000, %1
+  %2 = load ptr, ptr %handle.addr, align 4
+  %a1 = getelementptr inbounds %struct.dummy_t, ptr %2, i32 0, i32 0
+  %3 = load float, ptr %a1, align 4
+  %4 = call float @llvm.fmuladd.f32(float 0x3F847AE140000000, float %sub, float %3)
+  store float %4, ptr %a1, align 4
+  %5 = load ptr, ptr %handle.addr, align 4
+  %b = getelementptr inbounds %struct.dummy_t, ptr %5, i32 0, i32 1
+  %6 = load float, ptr %b, align 4
+  %sub2 = fsub float 0x3F5439DE40000000, %6
+  %7 = load ptr, ptr %handle.addr, align 4
+  %b3 = getelementptr inbounds %struct.dummy_t, ptr %7, i32 0, i32 1
+  %8 = load float, ptr %b3, align 4
+  %9 = call float @llvm.fmuladd.f32(float 0x3F947AE140000000, float %sub2, float %8)
+  store float %9, ptr %b3, align 4
+  %10 = load ptr, ptr %handle.addr, align 4
+  %c = getelementptr inbounds %struct.dummy_t, ptr %10, i32 0, i32 2
+  %11 = load float, ptr %c, align 4
+  %sub4 = fsub float 0x3F5439DE40000000, %11
+  %12 = load ptr, ptr %handle.addr, align 4
+  %c5 = getelementptr inbounds %struct.dummy_t, ptr %12, i32 0, i32 2
+  %13 = load float, ptr %c5, align 4
+  %14 = call float @llvm.fmuladd.f32(float 0x3F9EB851E0000000, float %sub4, float %13)
+  store float %14, ptr %c5, align 4
+  %15 = load ptr, ptr %handle.addr, align 4
+  %d = getelementptr inbounds %struct.dummy_t, ptr %15, i32 0, i32 3
+  %16 = load float, ptr %d, align 4
+  %sub6 = fsub float 0x3F5439DE40000000, %16
+  %17 = load ptr, ptr %handle.addr, align 4
+  %d7 = getelementptr inbounds %struct.dummy_t, ptr %17, i32 0, i32 3
+  %18 = load float, ptr %d7, align 4
+  %19 = call float @llvm.fmuladd.f32(float 0x3FA47AE140000000, float %sub6, float %18)
+  store float %19, ptr %d7, align 4
+  ret i8 0
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DavidSpickett wrote:

Ok I see, you need to setup the call to this fmuladd, that you know will emit MVE instructions.

In that case, could you add a check line for one of the MVE instructions as well? That would make the intent clearer, and warn us in the (unlikely) case that this code stopped emitting MVE instructions.

https://github.com/llvm/llvm-project/pull/71545