[llvm-branch-commits] [llvm] 81c9639 - [MC] Recalculate fragment offsets after relaxation

[Jian Cai via llvm-branch-commits]

Author: Jian Cai
Date: 2020-03-17T14:27:47-07:00
New Revision: 81c9639ebafc42f90f6e0b83ec01e70d86558e06

URL: https://github.com/llvm/llvm-project/commit/81c9639ebafc42f90f6e0b83ec01e70d86558e06
DIFF: https://github.com/llvm/llvm-project/commit/81c9639ebafc42f90f6e0b83ec01e70d86558e06.diff

LOG: [MC] Recalculate fragment offsets after relaxation

Summary:
The current relaxation implementation is not correctly adjusting the
size and offsets of fragements in one section based on changes in size
of another if the layout order of the two happened to be such that the
former was visited before the later. Therefore, we need to invalidate
the fragments in all sections after each iteration of relaxation, and
possibly further relax some of them in the next ieration. This fixes
PR#45190.

Reviewers: jyknight, MaskRay, annita.zhang, reames, skan

Reviewed By: reames, skan

Subscribers: llozano, manojgupta, nickdesaulniers, hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D76114

Added: 
    llvm/test/MC/X86/relax-offset.s

Modified: 
    llvm/lib/MC/MCAssembler.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/MC/MCAssembler.cpp b/llvm/lib/MC/MCAssembler.cpp
index 83f0d62bac2a..97fb13bdb885 100644
--- a/llvm/lib/MC/MCAssembler.cpp
+++ b/llvm/lib/MC/MCAssembler.cpp
@@ -785,9 +785,15 @@ void MCAssembler::layout(MCAsmLayout &Layout) {
   }
 
   // Layout until everything fits.
-  while (layoutOnce(Layout))
+  while (layoutOnce(Layout)) {
     if (getContext().hadError())
       return;
+    // Size of fragments in one section can depend on the size of fragments in
+    // another. If any fragment has changed size, we have to re-layout (and
+    // as a result possibly further relax) all.
+    for (MCSection &Sec : *this)
+      Layout.invalidateFragmentsFrom(&*Sec.begin());
+  }
 
   DEBUG_WITH_TYPE("mc-dump", {
       errs() << "assembler backend - post-relaxation\n--\n";

diff  --git a/llvm/test/MC/X86/relax-offset.s b/llvm/test/MC/X86/relax-offset.s
new file mode 100644
index 000000000000..78de255e9d6f
--- /dev/null
+++ b/llvm/test/MC/X86/relax-offset.s
@@ -0,0 +1,13 @@
+# RUN: llvm-mc -filetype=obj -triple=i386 %s | llvm-objdump - --headers | FileCheck %s
+
+  # CHECK: .text1        00000005 00000000
+  # CHECK: .text2        00000005 00000000
+
+  .section .text1
+ .skip after-before,0x0
+.Lint80_keep_stack:
+
+  .section .text2
+before:
+ jmp .Lint80_keep_stack
+after: