[PATCH] D36616: [mips] Handle variables with an explicit section and interactions with .sdata, .sbss

[Simon Dardis via Phabricator via llvm-commits]

sdardis created this revision.
Herald added a subscriber: arichardson.

If a variable has an explicit section such as .sdata or .sbss, it is placed
in that section and accessed in a gp relative manner. This overrides the global
-G setting.

Otherwise if a variable has a explicit section attached to it, such as '.rodata'
or '.mysection', it is not placed in the small data section. This also overrides
the global -G setting.


Repository:
  rL LLVM

https://reviews.llvm.org/D36616

Files:
  lib/Target/Mips/MipsTargetObjectFile.cpp
  test/CodeGen/Mips/gpopt-explict-section.ll


Index: test/CodeGen/Mips/gpopt-explict-section.ll
===================================================================
--- /dev/null
+++ test/CodeGen/Mips/gpopt-explict-section.ll
@@ -0,0 +1,53 @@
+; RUN: llc < %s -march=mips -mcpu=mips32 -mips-ssection-threshold=8 \
+; RUN:     -relocation-model=static -mattr=+noabicalls -mgpopt \
+; RUN:   | FileCheck %s
+
+; Test that object with an explicit section that is not .sdata or .sbss are not
+; considered in the small data section if they would otherwise qualify to be in
+; small data section. Also test that explicitly placing something in the small
+; data section uses %gp_rel addressing mode.
+
+ at a = global [2 x i32] zeroinitializer, section ".rodata", align 4
+ at b = global [4 x i32] zeroinitializer, section ".sdata", align 4
+ at c = global [4 x i32] zeroinitializer, section ".sbss", align 4
+
+; CHECK-LABEL: g
+; CHECK:       lui $[[R:[0-9]+]], %hi(a)
+; CHECK:       lw  ${{[0-9]+}}, %lo(a)($[[R]])
+
+define i32 @g() {
+entry:
+  %0 = load i32, i32* getelementptr inbounds ([2 x i32], [2 x i32]* @a, i32 0, i32 0), align 4
+  ret i32 %0
+}
+
+; CHECK-LABEL: f:
+; CHECK-LABEL: lw ${{[0-9]+}}, %gp_rel(b)($gp)
+
+define i32 @f() {
+entry:
+  %0 = load i32, i32* getelementptr inbounds ([4 x i32], [4 x i32]* @b, i32 0, i32 0), align 4
+  ret i32 %0
+}
+
+; CHECK-LABEL: h:
+; CHECK-LABEL: lw ${{[0-9]+}}, %gp_rel(c)($gp)
+
+define i32 @h() {
+entry:
+  %0 = load i32, i32* getelementptr inbounds ([4 x i32], [4 x i32]* @c, i32 0, i32 0), align 4
+  ret i32 %0
+}
+
+
+; CHECK:  .type a, at object
+; CHECK:  .section  .rodata,"a", at progbits
+; CHECK:  .globl  a
+
+; CHECK:  .type b, at object
+; CHECK:  .section  .sdata,"aw", at progbits
+; CHECK:  .globl  b
+
+; CHECK:  .type c, at object
+; CHECK:  .section  .sbss,"aw", at nobits
+; CHECK:  .globl  c
Index: lib/Target/Mips/MipsTargetObjectFile.cpp
===================================================================
--- lib/Target/Mips/MipsTargetObjectFile.cpp
+++ lib/Target/Mips/MipsTargetObjectFile.cpp
@@ -106,6 +106,22 @@
   if (!GVA)
     return false;
 
+  // If the variable has an explicit section, it is placed in that section but
+  // it's addressing mode may change.
+  if (GVA->hasSection()) {
+    StringRef Section = GVA->getSection();
+
+    // Explicitly placing any variable in the small data section overrides
+    // the global -G value.
+    if (Section == ".sdata" || Section == ".sbss")
+      return true;
+
+    // Otherwise reject accessing it through the gp pointer. There are some
+    // historic cases which GCC doesn't appear to respect any more. These
+    // are .lit4, .lit8 and .srdata. For the moment reject these as well.
+    return false;
+  }
+
   // Enforce -mlocal-sdata.
   if (!LocalSData && GVA->hasLocalLinkage())
     return false;


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