[llvm] r268662 - ARM: don't attempt to merge litpools referencing different PC-anchors.

[Tim Northover via llvm-commits]

Author: tnorthover
Date: Thu May  5 13:38:53 2016
New Revision: 268662

URL: http://llvm.org/viewvc/llvm-project?rev=268662&view=rev
Log:
ARM: don't attempt to merge litpools referencing different PC-anchors.

Given something like:

    ldr r0, .LCPI0_0 (== pc-rel var)
    add r0, pc

    ldr r1, .LCPI0_1 (== pc-rel var)
    add r1, pc

we cannot combine the 2 ldr instructions and litpools because they get added to
a different pc to form the correct address. I think the original logic came
from a time when we fused the LDRpci/PICADD instructions into one
pseudo-instruction so the PC was always immediately at-hand. That's no longer
the case.

Should fix general-dynamic TLS access on Linux, and quite possibly other -fPIC
code that relies on litpools (e.g. v6m and -Oz compilations) though trivial
tweaks of the .ll test didn't provoke anything.

Added:
    llvm/trunk/test/CodeGen/ARM/litpool-licm.ll
Modified:
    llvm/trunk/lib/Target/ARM/ARMConstantPoolValue.cpp

Modified: llvm/trunk/lib/Target/ARM/ARMConstantPoolValue.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Target/ARM/ARMConstantPoolValue.cpp?rev=268662&r1=268661&r2=268662&view=diff
==============================================================================
--- llvm/trunk/lib/Target/ARM/ARMConstantPoolValue.cpp (original)
+++ llvm/trunk/lib/Target/ARM/ARMConstantPoolValue.cpp Thu May  5 13:38:53 2016
@@ -74,9 +74,9 @@ bool
 ARMConstantPoolValue::hasSameValue(ARMConstantPoolValue *ACPV) {
   if (ACPV->Kind == Kind &&
       ACPV->PCAdjust == PCAdjust &&
-      ACPV->Modifier == Modifier) {
-    if (ACPV->LabelId == LabelId)
-      return true;
+      ACPV->Modifier == Modifier &&
+      ACPV->LabelId == LabelId &&
+      ACPV->AddCurrentAddress == AddCurrentAddress) {
     // Two PC relative constpool entries containing the same GV address or
     // external symbols. FIXME: What about blockaddress?
     if (Kind == ARMCP::CPValue || Kind == ARMCP::CPExtSymbol)

Added: llvm/trunk/test/CodeGen/ARM/litpool-licm.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/ARM/litpool-licm.ll?rev=268662&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/ARM/litpool-licm.ll (added)
+++ llvm/trunk/test/CodeGen/ARM/litpool-licm.ll Thu May  5 13:38:53 2016
@@ -0,0 +1,46 @@
+; RUN: llc -mtriple=thumbv7-linux-gnueabihf -relocation-model=pic %s -o - | FileCheck %s
+
+ at var = thread_local global i32 0, align 4
+
+define void @func(i32 %n) {
+; CHECK-LABEL: func:
+; CHECK: ldr [[REF1:r[0-9]+]], [[CP1:.LCPI[0-9]+_[0-9]+]]
+; CHECK: ldr [[REF2:r[0-9]+]], [[CP2:.LCPI[0-9]+_[0-9]+]]
+
+; CHECK: [[PCPOS1:.LPC[0-9]+_[0-9]+]]:
+; CHECK-NEXT: add [[REF1]], pc
+
+; CHECK: [[PCPOS2:.LPC[0-9]+_[0-9]+]]:
+; CHECK-NEXT: add [[REF2]], pc
+
+; CHECK: [[CP1]]:
+; CHECK-NEXT: [[CP1_TMP:.Ltmp[0-9]+]]:
+; CHECK-NEXT:     .long var(TLSGD)-(([[PCPOS1]]+4)-[[CP1_TMP]])
+
+; CHECK: [[CP2]]:
+; CHECK-NEXT: [[CP2_TMP:.Ltmp[0-9]+]]:
+; CHECK-NEXT:     .long var(TLSGD)-(([[PCPOS2]]+4)-[[CP2_TMP]])
+
+entry:
+  br label %loop
+
+loop:
+  %i = phi i32 [ %inc, %next ], [ 0, %entry ]
+  %val = load i32, i32* @var
+  %tst = icmp eq i32 %val, 0
+  br i1 %tst, label %next, label %call
+
+call:
+  tail call void @foo(i32* nonnull @var) #2
+  br label %next
+
+next:
+  %inc = add i32 %i, 1
+  %stop = icmp eq i32 %inc, %n
+  br i1 %stop, label %done, label %loop
+
+done:
+  ret void
+}
+
+declare void @foo(i32*)
\ No newline at end of file