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[Mips][MC] AttemptToFoldSymbolOffsetDifference: revert isMicroMips special case

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D52985/D57677 added a .gcc_except_table workaround, but the new behavior
doesn't match GNU assembler.
```
void foo();
int bar() {
  foo();
  try { throw 1; }
  catch (int) { return 1; }
  return 0;
}

clang --target=mipsel-linux-gnu -mmicromips -S a.cc
mipsel-linux-gnu-gcc -mmicromips -c a.s -o gnu.o

.uleb128 ($cst_end0)-($cst_begin0)     // bit 0 is not forced to 1
.uleb128 ($func_begin0)-($func_begin0) // bit 0 is not forced to 1
```

I have inspected `.gcc_except_table` output by `mipsel-linux-gnu-gcc -mmicromips -c a.cc`.
The `.uleb128` values are not forced to set the least significant bit.

In addition, D57677's adjustment (even->odd) to CodeGen/Mips/micromips-b-range.ll is wrong.
PC-relative `.long func - .` values will differ from GNU assembler as well.

The original intention of D52985 seems unclear to me. I think whatever
goal it wants to achieve should be moved to an upper layer.

This isMicroMips special case has caused problems to fix MCAssembler::relaxLEB to use evaluateAsAbsolute instead of evaluateKnownAbsolute,
which is needed to proper support R_RISCV_SET_ULEB128/R_RISCV_SUB_ULEB128.

Differential Revision: https://reviews.llvm.org/D157655
This commit is contained in:
Fangrui Song
2023-08-16 23:11:59 -07:00
parent 235dad3328
commit 4c89277095
4 changed files with 7 additions and 12 deletions
Download Patch File Download Diff File Expand all files Collapse all files

5
llvm/lib/MC/MCExpr.cpp
View File

@@ -611,11 +611,6 @@ static void AttemptToFoldSymbolOffsetDifference(
if (Asm->isThumbFunc(&SA))
Addend |= 1;
// If symbol is labeled as micromips, we set low-bit to ensure
// correct offset in .gcc_except_table
if (Asm->getBackend().isMicroMips(&SA))
Addend |= 1;
// Clear the symbol expr pointers to indicate we have folded these
// operands.
A = B = nullptr;

8
llvm/test/CodeGen/Mips/micromips-b-range.ll
View File

@@ -13,7 +13,7 @@
; CHECK-NEXT: 1e: fb fd 00 00 sw $ra, 0($sp)
; CHECK-NEXT: 22: 41 a1 00 01 lui $1, 1
; CHECK-NEXT: 26: 40 60 00 02 bal 0x2e <foo+0x2e>
; CHECK-NEXT: 2a: 30 21 04 69 addiu $1, $1, 1129
; CHECK-NEXT: 2a: 30 21 04 68 addiu $1, $1, 1128
; CHECK-NEXT: 2e: 00 3f 09 50 addu $1, $ra, $1
; CHECK-NEXT: 32: ff fd 00 00 lw $ra, 0($sp)
; CHECK-NEXT: 36: 00 01 0f 3c jr $1
@@ -27,7 +27,7 @@
; CHECK-NEXT: 56: fb fd 00 00 sw $ra, 0($sp)
; CHECK-NEXT: 5a: 41 a1 00 01 lui $1, 1
; CHECK-NEXT: 5e: 40 60 00 02 bal 0x66 <foo+0x66>
; CHECK-NEXT: 62: 30 21 04 5d addiu $1, $1, 1117
; CHECK-NEXT: 62: 30 21 04 5c addiu $1, $1, 1116
; CHECK-NEXT: 66: 00 3f 09 50 addu $1, $ra, $1
; CHECK-NEXT: 6a: ff fd 00 00 lw $ra, 0($sp)
; CHECK-NEXT: 6e: 00 01 0f 3c jr $1
@@ -39,7 +39,7 @@
; CHECK-NEXT: 86: fb fd 00 00 sw $ra, 0($sp)
; CHECK-NEXT: 8a: 41 a1 00 01 lui $1, 1
; CHECK-NEXT: 8e: 40 60 00 02 bal 0x96 <foo+0x96>
; CHECK-NEXT: 92: 30 21 04 2d addiu $1, $1, 1069
; CHECK-NEXT: 92: 30 21 04 2c addiu $1, $1, 1068
; CHECK-NEXT: 96: 00 3f 09 50 addu $1, $ra, $1
; CHECK-NEXT: 9a: ff fd 00 00 lw $ra, 0($sp)
; CHECK-NEXT: 9e: 00 01 0f 3c jr $1
@@ -51,7 +51,7 @@
; CHECK-NEXT: 10476: fb fd 00 00 sw $ra, 0($sp)
; CHECK-NEXT: 1047a: 41 a1 00 01 lui $1, 1
; CHECK-NEXT: 1047e: 40 60 00 02 bal 0x10486 <foo+0x10486>
; CHECK-NEXT: 10482: 30 21 04 01 addiu $1, $1, 1025
; CHECK-NEXT: 10482: 30 21 04 00 addiu $1, $1, 1024
; CHECK-NEXT: 10486: 00 3f 09 50 addu $1, $ra, $1
; CHECK-NEXT: 1048a: ff fd 00 00 lw $ra, 0($sp)
; CHECK-NEXT: 1048e: 00 01 0f 3c jr $1

2
llvm/test/CodeGen/Mips/micromips-gcc-except-table.ll
View File

@@ -1,7 +1,7 @@
; RUN: llc -mtriple=mips-linux-gnu -mcpu=mips32r2 -mattr=+micromips -O3 -filetype=obj < %s | llvm-objdump -s -j .gcc_except_table - | FileCheck %s
; CHECK: Contents of section .gcc_except_table:
; CHECK-NEXT: 0000 ff9b1501 0c011100 00110e1f 011f1800
; CHECK-NEXT: 0000 ff9b1501 0c001000 00100e1e 011e1800
; CHECK-NEXT: 0010 00010000 00000000
@_ZTIi = external constant ptr

4
llvm/test/DebugInfo/Mips/eh_frame.ll
View File

@@ -26,9 +26,9 @@
; CHECK-READELF-PIC-NEXT: R_MIPS_PC32
; CHECK-READELF-NEXT: .gcc_except_table
; EXCEPT-TABLE-STATIC: 0000 ff9b1501 0c011500 00150e23 01231e00 ...........#.#..
; EXCEPT-TABLE-STATIC: 0000 ff9b1501 0c001400 00140e22 01221e00 ..........."."..
; EXCEPT-TABLE-STATIC: 0010 00010000 00000000
; EXCEPT-TABLE-PIC: 0000 ff9b1501 0c012d00 002d133f 013f2a00 ......-..-.?.?*.
; EXCEPT-TABLE-PIC: 0000 ff9b1501 0c002c00 002c123e 013e2a00 ......,..,.>.>*.
; EXCEPT-TABLE-PIC: 0010 00010000 00000000 ........
@_ZTIi = external constant ptr