[lld] [LLD] Implement --enable-non-contiguous-regions (PR #90007)

[Fangrui Song via llvm-commits]

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+# REQUIRES: x86
+
+# RUN: rm -rf %t && split-file %s %t && cd %t
+# RUN: llvm-mc -n -filetype=obj -triple=x86_64 spill.s -o spill.o
+
+## An input section spills to a later match when the region of its first match
+## would overflow. The spill uses the alignment of the later match.
+
+# RUN: ld.lld -T spill.ld spill.o -o spill --enable-non-contiguous-regions
+# RUN: llvm-readelf -S spill | FileCheck %s --check-prefix=SPILL
+
+# SPILL:      Name          Type     Address          Off    Size
+# SPILL:      .first_chance PROGBITS 0000000000000000 001000 000001
+# SPILL-NEXT: .last_chance  PROGBITS 0000000000000008 001008 000002
+
+## A spill off the end still fails the link.
+
+# RUN: not ld.lld -T spill-fail.ld spill.o -o spill-fail --enable-non-contiguous-regions 2>&1 |\
+# RUN:   FileCheck %s --check-prefix=SPILL-FAIL --implicit-check-not=error:
+
+# SPILL-FAIL: error: section '.last_chance' will not fit in region 'b': overflowed by 2 bytes
+
+## The above spill still occurs when the LMA would overflow, even though the
+## VMA would fit.
+
+# RUN: ld.lld -T spill-lma.ld spill.o -o spill-lma --enable-non-contiguous-regions
+# RUN: llvm-readelf -S spill-lma | FileCheck %s --check-prefix=SPILL-LMA
+
+# SPILL-LMA:      Name          Type     Address          Off    Size
+# SPILL-LMA:      .first_chance PROGBITS 0000000000000000 001000 000001
+# SPILL-LMA-NEXT: .last_chance  PROGBITS 0000000000000003 001003 000002
+
+## A spill occurs to an additional match after the first.
+
+# RUN: ld.lld -T spill-later.ld spill.o -o spill-later --enable-non-contiguous-regions
+# RUN: llvm-readelf -S spill-later | FileCheck %s --check-prefix=SPILL-LATER
+
+# SPILL-LATER:      Name            Type     Address          Off    Size
+# SPILL-LATER:      .first_chance   PROGBITS 0000000000000000 001000 000001
+# SPILL-LATER-NEXT: .second_chance  PROGBITS 0000000000000002 001001 000000
+# SPILL-LATER-NEXT: .last_chance    PROGBITS 0000000000000003 001003 000002
+
+## A later overflow causes an earlier section to spill.
+
+# RUN: ld.lld -T spill-earlier.ld spill.o -o spill-earlier --enable-non-contiguous-regions
+# RUN: llvm-readelf -S spill-earlier | FileCheck %s --check-prefix=SPILL-EARLIER
+
+# SPILL-EARLIER:      Name          Type     Address          Off    Size
+# SPILL-EARLIER:      .first_chance PROGBITS 0000000000000000 001000 000002
+# SPILL-EARLIER-NEXT: .last_chance  PROGBITS 0000000000000002 001002 000001
+
+## An additional match in /DISCARD/ has no effect.
+
+# RUN: not ld.lld -T no-spill-into-discard.ld spill.o -o no-spill-into-discard --enable-non-contiguous-regions 2>&1 |\
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MaskRay wrote:

`not ld.lld` commands can omit  `-o` (default: `a.out`) if `cd %t` has been invoked.

https://github.com/llvm/llvm-project/pull/90007