Implement ppc/ppc64 preserves_flags option for inline asm

Implemented preserves_flags similar to the `cc` pseudo-register
on gcc and clang.

The gcc inline documentation doesn't actually state what this
does on powerpc* targets, but inspection of the source shows
it is equivalent to condition register field `cr0`.

Author: pmur

compiler/rustc_codegen_llvm/src/asm.rs

@@ -251,7 +251,9 @@ impl<'ll, 'tcx> AsmBuilderMethods<'tcx> for Builder<'_, 'll, 'tcx> {
                     constraints.push("~{sreg}".to_string());
                 }
                 InlineAsmArch::Nvptx64 => {}
-                InlineAsmArch::PowerPC | InlineAsmArch::PowerPC64 => {}
+                InlineAsmArch::PowerPC | InlineAsmArch::PowerPC64 => {
+                    constraints.push("~{cr0}".to_string());
+                }
                 InlineAsmArch::Hexagon => {}
                 InlineAsmArch::LoongArch32 | InlineAsmArch::LoongArch64 => {
                     constraints.extend_from_slice(&[

src/doc/unstable-book/src/language-features/asm-experimental-arch.md

@@ -201,6 +201,8 @@ These flags registers must be restored upon exiting the asm block if the `preser
   - The status register `r2`.
 - M68k
   - The condition code register `ccr`.
+- PowerPC
+  - The condition register field `cr0`
 - SPARC
   - Integer condition codes (`icc` and `xcc`)
   - Floating-point condition codes (`fcc[0-3]`)

tests/codegen-llvm/asm/powerpc-clobbers.rs

@@ -77,3 +77,37 @@ pub unsafe fn vs32_clobber() {
 pub unsafe fn clobber_abi() {
     asm!("", clobber_abi("C"), options(nostack, nomem, preserves_flags));
 }
+
+// CHECK-LABEL: @clobber_no_preserves_flags
+// CHECK: call void asm sideeffect "nop", "~{cr0}"()
+#[no_mangle]
+pub unsafe fn clobber_no_preserves_flags() {
+    // Use a nop to prevent aliasing of identical functions here.
+    asm!("nop", options(nostack, nomem));
+}
+
+// CHECK-LABEL: @cr0_clobber_no_preserves_flags
+// CHECK: call void asm sideeffect "nop; nop", "~{cr0},~{cr0}"()
+#[no_mangle]
+pub unsafe fn cr0_clobber_no_preserves_flags() {
+    // Use nop; nop to prevent aliasing of identical functions here.
+    asm!("nop; nop", out("cr0") _, options(nostack, nomem));
+}
+
+// CHECK-LABEL: @clobber_preservesflags
+// CHECK: call void asm sideeffect "", "~{memory}"()
+#[no_mangle]
+pub unsafe fn clobber_preservesflags() {
+    asm!("", options(nostack, preserves_flags));
+}
+
+// Output format depends on the availability of altivec and vsx
+// CHECK-LABEL: @clobber_abi_no_preserves_flags
+#[no_mangle]
+// powerpc: asm sideeffect "", "={r0},={r3},={r4},={r5},={r6},={r7},={r8},={r9},={r10},={r11},={r12},={f0},={f1},={f2},={f3},={f4},={f5},={f6},={f7},={f8},={f9},={f10},={f11},={f12},={f13},~{vs0},~{vs1},~{vs2},~{vs3},~{vs4},~{vs5},~{vs6},~{vs7},~{vs8},~{vs9},~{vs10},~{vs11},~{vs12},~{vs13},~{vs14},~{vs15},~{vs16},~{vs17},~{vs18},~{vs19},~{vs20},~{vs21},~{vs22},~{vs23},~{vs24},~{vs25},~{vs26},~{vs27},~{vs28},~{vs29},~{vs30},~{vs31},~{v0},~{v1},~{v2},~{v3},~{v4},~{v5},~{v6},~{v7},~{v8},~{v9},~{v10},~{v11},~{v12},~{v13},~{v14},~{v15},~{v16},~{v17},~{v18},~{v19},~{cr0},~{cr1},~{cr5},~{cr6},~{cr7},~{ctr},~{lr},~{xer},~{cr0}"()
+// powerpc64: asm sideeffect "", "={r0},={r3},={r4},={r5},={r6},={r7},={r8},={r9},={r10},={r11},={r12},={f0},={f1},={f2},={f3},={f4},={f5},={f6},={f7},={f8},={f9},={f10},={f11},={f12},={f13},={v0},={v1},={v2},={v3},={v4},={v5},={v6},={v7},={v8},={v9},={v10},={v11},={v12},={v13},={v14},={v15},={v16},={v17},={v18},={v19},~{vs0},~{vs1},~{vs2},~{vs3},~{vs4},~{vs5},~{vs6},~{vs7},~{vs8},~{vs9},~{vs10},~{vs11},~{vs12},~{vs13},~{vs14},~{vs15},~{vs16},~{vs17},~{vs18},~{vs19},~{vs20},~{vs21},~{vs22},~{vs23},~{vs24},~{vs25},~{vs26},~{vs27},~{vs28},~{vs29},~{vs30},~{vs31},~{cr0},~{cr1},~{cr5},~{cr6},~{cr7},~{ctr},~{lr},~{xer},~{cr0}"()
+// powerpc64le: asm sideeffect "", "={r0},={r3},={r4},={r5},={r6},={r7},={r8},={r9},={r10},={r11},={r12},={f0},={f1},={f2},={f3},={f4},={f5},={f6},={f7},={f8},={f9},={f10},={f11},={f12},={f13},={vs0},={vs1},={vs2},={vs3},={vs4},={vs5},={vs6},={vs7},={vs8},={vs9},={vs10},={vs11},={vs12},={vs13},={vs14},={vs15},={vs16},={vs17},={vs18},={vs19},={vs20},={vs21},={vs22},={vs23},={vs24},={vs25},={vs26},={vs27},={vs28},={vs29},={vs30},={vs31},={v0},={v1},={v2},={v3},={v4},={v5},={v6},={v7},={v8},={v9},={v10},={v11},={v12},={v13},={v14},={v15},={v16},={v17},={v18},={v19},~{cr0},~{cr1},~{cr5},~{cr6},~{cr7},~{ctr},~{lr},~{xer},~{cr0}"()
+// aix64: asm sideeffect "", "={r0},={r3},={r4},={r5},={r6},={r7},={r8},={r9},={r10},={r11},={r12},={f0},={f1},={f2},={f3},={f4},={f5},={f6},={f7},={f8},={f9},={f10},={f11},={f12},={f13},={vs0},={vs1},={vs2},={vs3},={vs4},={vs5},={vs6},={vs7},={vs8},={vs9},={vs10},={vs11},={vs12},={vs13},={vs14},={vs15},={vs16},={vs17},={vs18},={vs19},={vs20},={vs21},={vs22},={vs23},={vs24},={vs25},={vs26},={vs27},={vs28},={vs29},={vs30},={vs31},={v0},={v1},={v2},={v3},={v4},={v5},={v6},={v7},={v8},={v9},={v10},={v11},={v12},={v13},={v14},={v15},={v16},={v17},={v18},={v19},~{cr0},~{cr1},~{cr5},~{cr6},~{cr7},~{ctr},~{lr},~{xer},~{cr0}"()
+pub unsafe fn clobber_abi_no_preserves_flags() {
+    asm!("", clobber_abi("C"), options(nostack, nomem));
+}