[PPC][InlineASM] Mark the 'a' constraint as unsupported

[kamaub]

'a' is an input/ouput constraint for restraining assembly variables
to an indexed or indirect address operand. It previously was marked
as supported but would throw an assertion for unknown constraint type
in the back-end when this test case was compiled. This change marks it
as unsupported until we can add full support for address operands
constraining to the compiler code generation.

[llvmbot]

@llvm/pr-subscribers-backend-powerpc

@llvm/pr-subscribers-clang

Author: Kamau Bridgeman (kamaub)

Changes

'a' is an input/ouput constraint for restraining assembly variables
to an indexed or indirect address operand. It previously was marked
as supported but would throw an assertion for unknown constraint type
in the back-end when this test case was compiled. This change marks it
as unsupported until we can add full support for address operands
constraining to the compiler code generation.

---

Full diff: https://github.com/llvm/llvm-project/pull/96109.diff

2 Files Affected:

• (modified) clang/lib/Basic/Targets/PPC.h (+3-1)
• (added) clang/test/CodeGen/PowerPC/inline-asm-unsupported-constraint-error.c (+8)

diff --git a/clang/lib/Basic/Targets/PPC.h b/clang/lib/Basic/Targets/PPC.h
index fc23c30c68523..e4d6a02386da5 100644
--- a/clang/lib/Basic/Targets/PPC.h
+++ b/clang/lib/Basic/Targets/PPC.h
@@ -305,9 +305,11 @@ class LLVM_LIBRARY_VISIBILITY PPCTargetInfo : public TargetInfo {
               // asm statements)
       Info.setAllowsMemory();
       break;
-    case 'R': // AIX TOC entry
     case 'a': // Address operand that is an indexed or indirect from a
               // register (`p' is preferable for asm statements)
+              // TODO: Add full support for this constraint
+      return false;
+    case 'R': // AIX TOC entry
     case 'S': // Constant suitable as a 64-bit mask operand
     case 'T': // Constant suitable as a 32-bit mask operand
     case 'U': // System V Release 4 small data area reference
diff --git a/clang/test/CodeGen/PowerPC/inline-asm-unsupported-constraint-error.c b/clang/test/CodeGen/PowerPC/inline-asm-unsupported-constraint-error.c
new file mode 100644
index 0000000000000..457908f016b0c
--- /dev/null
+++ b/clang/test/CodeGen/PowerPC/inline-asm-unsupported-constraint-error.c
@@ -0,0 +1,8 @@
+// RUN: %clang_cc1 -emit-llvm -triple powerpc64le-unknown-unknown -verify %s
+// This test case exist to test marking the 'a' inline assembly constraint as
+// unsupported because powerpc previously marked it as supported.
+int foo(int arg){
+  asm goto ("bc %0,%1,%l[TEST_LABEL]" : : "a"(&&TEST_LABEL) : : TEST_LABEL); //expected-error {{invalid input constraint 'a' in asm}}
+  return 0;
+TEST_LABEL: return arg + 1;
+}

[chenzheng1030]

LGTM except a nit.

[chenzheng1030]

nit: can you also add run lines for AIX 32 and 64 bit?

[MaskRay]

I think one RUN line (powerpc64) is sufficient. Duplicating this for ELF/XCOFF isn't necessary.

inline-asm-constraints-error.c might be a better test name. You can reuse the test for other errors.