Add Percent Symbol Before Named PPC Registers

[tjablin]

Summary

The -ppc-asm-full-reg-names flag causes LLVM to generate named PPC registers instead of numbers. However, the resulting assembly code was not parsable by either GCC or LLVM due to missing percent symbols before register names. This patch inserts a percent sign before register names on PPC when -ppc-asm-full-reg-names is enabled except for the registers PPC::ZERO and other special registers that do not require the percent symbol.

[gut]

Hi. This change seems interesting, why wasn't it reviewed?

Our team is considering implementing such a thing for POWER8 but then we noticed this patch.

[nemanjai]

In D22948#892973, @gut wrote:

Hi. This change seems interesting, why wasn't it reviewed?

Our team is considering implementing such a thing for POWER8 but then we noticed this patch.

The author never pinged it and it dropped off of people's radar. Is this of interest to you? The option that this helps with is seldom used - and only in testing, so this wasn't anyone's top priority. If you'd like to see this through, commandeer the patch, update it so it applies to (and passes all tests on) trunk and re-post.
I don't expect any of the reviewers will have an issue approving it.

[gut]

Alright, thanks for letting us know that there was no implicit rejection to this kind of functionality. We'll take a closer look and commandeer this review when the other review is available.

lib/Target/PowerPC/InstPrinter/PPCInstPrinter.cpp

 void PPCInstPrinter::printOperand(const MCInst *MI, unsigned OpNo,
                                   raw_ostream &O) {
   const MCOperand &Op = MI->getOperand(OpNo);
   if (Op.isReg()) {
     const char *RegName = getRegisterName(Op.getReg());
     // The linux and AIX assembler does not take register prefixes.
     if (!isDarwinSyntax())
       RegName = stripRegisterPrefix(RegName);
-    
+    if (FullRegNames && !isDarwinSyntax() &&
+        Op.getReg() != PPC::ZERO && Op.getReg() < PPC::ZERO8)
+      O << '%';
+    
     O << RegName;
     return;
   }
   
   if (Op.isImm()) {
     O << Op.getImm();
     return;
   }
   
   assert(Op.isExpr() && "unknown operand kind in printOperand");
   Op.getExpr()->print(O, &MAI);
 }
 

test/CodeGen/PowerPC/reg-names.ll

 ; RUN: llc -mtriple=powerpc64-unknown-linux-gnu < %s | FileCheck %s
 ; RUN: llc -mtriple=powerpc64-unknown-linux-gnu -ppc-asm-full-reg-names < %s | FileCheck -check-prefix=CHECK-FN %s
 
 define i64 @test1(i64 %a, i64 %b) {
 ; CHECK-LABEL: @test1
 ; CHECK-FN-LABEL: @test1
 
 entry:
   ret i64 %b
 
 ; CHECK: mr 3, 4
-; CHECK-FN: mr r3, r4
+; CHECK-FN: mr %r3, %r4
+
+; CHECK: blr
+; CHECK-FN: blr
+}
+
+define i64 @test2(i64 %a, i64 %b) {
+; CHECK-LABEL: @test2
+; CHECK-FN-LABEL: @test2
+
+entry:
+  ret i64 0
+
+; CHECK: li 3, 0
+; CHECK-FN: li %r3, 0
 
 ; CHECK: blr
 ; CHECK-FN: blr
 }