[llvm][PowerPC] Add missing support for 'I' asm template argument modifiers

[tbaeder]

Summary

I is already documented as being supported but was not implemented. Add the missing case for it and a test case.

This is after review in https://bugs.llvm.org/show_bug.cgi?id=50608

[nemanjai]

I am sorry, my suggestion turned out to be wrong. I have suggested the fix in the original bug (and please add the IR for the motivating test case).

[nemanjai]

LGTM with a simplification to the test case.

llvm/test/CodeGen/PowerPC/asm-template-I.ll

1 ↗

(On Diff #351070)

We can simplify this test case and add checks rather than just expecting a successful execution. The entire test can be simplified to:

; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc -verify-machineinstrs < %s -mtriple=powerpc64le-- | FileCheck %s
; https://bugs.llvm.org/show_bug.cgi?id=50608

define dso_local signext i32 @main(i32 signext %argc, i8** %argv) {
; CHECK-LABEL: main:
; CHECK:       # %bb.0: # %entry
; CHECK-NEXT:    stw 3, -4(1)
; CHECK-NEXT:    li 3, 0
; CHECK-NEXT:    addi 4, 1, -4
; CHECK-NEXT:    #APP
; CHECK-NEXT:    .ascii "-1@0(4)"
; CHECK-NEXT:    .byte 0
; CHECK-NEXT:    #NO_APP
; CHECK-NEXT:    blr
entry:
  call void asm sideeffect " .asciz \22${0:n}@${1:I}$1\22 ", "n,nZr"(i32 1, i32 %argc)
  ret i32 0
}

llvm/docs/LangRef.rst

 
 - ``L``: Print the second register of a two-register operand. Requires that it
   has been allocated consecutively to the first.
 
   .. FIXME: why is it restricted to consecutive ones? And there's
      nothing that ensures that happens, is there?
 
 - ``I``: Print the letter 'i' if the operand is an integer constant, otherwise
-  nothing. Used to print 'addi' vs 'add' instructions.
+  nothing. Used to print 'addi' vs 'add' instructions. (NOTE: This will currently
+  always print nothing)
 - ``y``: For a memory operand, prints formatter for a two-register X-form
   instruction. (Currently always prints ``r0,OPERAND``).
 - ``U``: Prints 'u' if the memory operand is an update form, and nothing
   otherwise. (NOTE: LLVM does not support update form, so this will currently
   always print nothing)
 - ``X``: Prints 'x' if the memory operand is an indexed form. (NOTE: LLVM does
   not support indexed form, so this will currently always print nothing)
 

llvm/lib/Target/PowerPC/PPCAsmPrinter.cpp

case 'L': // A memory reference to the upper word of a double word op.
       O << getDataLayout().getPointerSize() << "(";
       printOperand(MI, OpNo, O);
       O << ")";
       return false;
     case 'y': // A memory reference for an X-form instruction
       O << "0, ";
       printOperand(MI, OpNo, O);
       return false;
+    case 'I': // Print 'i' for integer constant.
     case 'U': // Print 'u' for update form.
     case 'X': // Print 'x' for indexed form.
       // FIXME: Currently for PowerPC memory operands are always loaded
       // into a register, so we never get an update or indexed form.
       // This is bad even for offset forms, since even if we know we
       // have a value in -16(r1), we will generate a load into r<n>
       // and then load from 0(r<n>).  Until that issue is fixed,
       // tolerate 'U' and 'X' but don't output anything.