Avoid emitting a PIC base register if no PIC addresses are needed.

This fixes rdar://8396318.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@114201 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 31 insertions, 2 deletions

diff --git a/lib/Target/X86/X86InstrInfo.cpp b/lib/Target/X86/X86InstrInfo.cpp
index 5280940cf4..e0165e11b8 100644
--- a/lib/Target/X86/X86InstrInfo.cpp
+++ b/lib/Target/X86/X86InstrInfo.cpp
@@ -3108,6 +3108,13 @@ namespace {
       if (TM->getRelocationModel() != Reloc::PIC_)
         return false;
 
+      X86MachineFunctionInfo *X86FI = MF.getInfo<X86MachineFunctionInfo>();
+      unsigned GlobalBaseReg = X86FI->getGlobalBaseReg();
+
+      // If we didn't need a GlobalBaseReg, don't insert code.
+      if (GlobalBaseReg == 0)
+        return false;
+
       // Insert the set of GlobalBaseReg into the first MBB of the function
       MachineBasicBlock &FirstMBB = MF.front();
       MachineBasicBlock::iterator MBBI = FirstMBB.begin();
@@ -3119,7 +3126,7 @@ namespace {
       if (TM->getSubtarget<X86Subtarget>().isPICStyleGOT())
         PC = RegInfo.createVirtualRegister(X86::GR32RegisterClass);
       else
-        PC = TII->getGlobalBaseReg(&MF);
+        PC = GlobalBaseReg;
   
       // Operand of MovePCtoStack is completely ignored by asm printer. It's
       // only used in JIT code emission as displacement to pc.
@@ -3128,7 +3135,6 @@ namespace {
       // If we're using vanilla 'GOT' PIC style, we should use relative addressing
       // not to pc, but to _GLOBAL_OFFSET_TABLE_ external.
       if (TM->getSubtarget<X86Subtarget>().isPICStyleGOT()) {
-        unsigned GlobalBaseReg = TII->getGlobalBaseReg(&MF);
         // Generate addl $__GLOBAL_OFFSET_TABLE_ + [.-piclabel], %some_register
         BuildMI(FirstMBB, MBBI, DL, TII->get(X86::ADD32ri), GlobalBaseReg)
           .addReg(PC).addExternalSymbol("_GLOBAL_OFFSET_TABLE_",
diff --git a/test/CodeGen/X86/fast-isel-avoid-unnecessary-pic-base.ll b/test/CodeGen/X86/fast-isel-avoid-unnecessary-pic-base.ll
new file mode 100644
index 0000000000..9233d3f7c1
--- /dev/null
+++ b/test/CodeGen/X86/fast-isel-avoid-unnecessary-pic-base.ll
@@ -0,0 +1,23 @@
+; RUN: llc -O0 -relocation-model=pic < %s | not grep call
+; rdar://8396318
+
+; Don't emit a PIC base register if no addresses are needed.
+
+target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128-n8:16:32"
+target triple = "i386-apple-darwin11.0.0"
+
+define i32 @foo(i32 %x, i32 %y, i32 %z) nounwind ssp {
+entry:
+  %x.addr = alloca i32, align 4
+  %y.addr = alloca i32, align 4
+  %z.addr = alloca i32, align 4
+  store i32 %x, i32* %x.addr, align 4
+  store i32 %y, i32* %y.addr, align 4
+  store i32 %z, i32* %z.addr, align 4
+  %tmp = load i32* %x.addr, align 4
+  %tmp1 = load i32* %y.addr, align 4
+  %add = add nsw i32 %tmp, %tmp1
+  %tmp2 = load i32* %z.addr, align 4
+  %add3 = add nsw i32 %add, %tmp2
+  ret i32 %add3
+}