[mips] Extend MipsAsmParser class to handle %got(sym + const) expressions

[atanasyan]

Summary

Now the parser supports %got(sym) expressions only but %got(sym + const) variant is also valid and accepted by GAS.

[• rafael]

LGTM, but can you make the test more specific? The current one passes if I change 1004 to 1003 for example.

[atanasyan]

In D16885#344953, @rafael wrote:

LGTM, but can you make the test more specific? The current one passes if I change 1004 to 1003 for example.

Thanks for review.

Do you change first or second or both 0x10004? If you change only the first one in the lw instruction, it is expected that the test passes because %got() takes upper 16-bits of the value. I use two instructions and two relocations in the test because such pair of relocations is a common case in the code.

[atanasyan]

Ping?

[llvm-commits]

LGTM

lib/Target/Mips/AsmParser/MipsAsmParser.cpp

if (const MCConstantExpr *MCE = dyn_cast<MCConstantExpr>(Expr)) {
     // It's a constant, evaluate reloc value.
     int16_t Val;
     switch (getVariantKind(RelocStr)) {
     case MCSymbolRefExpr::VK_Mips_ABS_LO:
       // Get the 1st 16-bits.
       Val = MCE->getValue() & 0xffff;
       break;
     case MCSymbolRefExpr::VK_Mips_ABS_HI:
+    case MCSymbolRefExpr::VK_Mips_GOT:
       // Get the 2nd 16-bits. Also add 1 if bit 15 is 1, to compensate for low
       // 16 bits being negative.
       Val = ((MCE->getValue() + 0x8000) >> 16) & 0xffff;
       break;
     case MCSymbolRefExpr::VK_Mips_HIGHER:
       // Get the 3rd 16-bits.
       Val = ((MCE->getValue() + 0x80008000LL) >> 32) & 0xffff;
       break;

test/MC/Mips/got-rel-expr.s

+# Check that llvm-mc accepts arithmetic expression
+# as an argument of the %got relocation.
+
+# RUN: llvm-mc -filetype=obj -triple=mips-unknown-linux %s \
+# RUN:   | llvm-objdump -d -r - | FileCheck %s
+
+  .text
+foo:
+  lw      $t0,%got($loc+0x10004)($gp)
+# CHECK: 0:       8f 88 00 01     lw      $8, 1($gp)
+# CHECK:                  00000000:  R_MIPS_GOT16 $loc
+  addi    $t0,$t0,%lo($loc+0x10004)
+# CHECK: 4:       21 08 00 04     addi    $8, $8, 4
+# CHECK:                  00000004:  R_MIPS_LO16  $loc
+
+  .data
+$loc:
+  .word 0
+  .space 0x10000
+  .word 0