[PATCH] Disable x86 tail call optimization under PIC mode

[Chih-Hung Hsieh]

Keep IsMustTail working as before.


http://reviews.llvm.org/D9799

Files:
  lib/Target/X86/X86ISelLowering.cpp
  test/CodeGen/X86/pic.ll
  test/CodeGen/X86/tail-call-got.ll
  test/CodeGen/X86/tailcallpic1.ll
  test/CodeGen/X86/tailcallpic2.ll

Index: lib/Target/X86/X86ISelLowering.cpp
===================================================================
--- lib/Target/X86/X86ISelLowering.cpp
+++ lib/Target/X86/X86ISelLowering.cpp
@@ -2752,11 +2752,15 @@
   if (MF.getTarget().Options.DisableTailCalls)
     isTailCall = false;
 
+  // Cannot jump to address through GOT, see https://llvm.org/bugs/show_bug.cgi?id=15086
+  if (Subtarget->isPICStyleGOT())
+    isTailCall = false;
+
   bool IsMustTail = CLI.CS && CLI.CS->isMustTailCall();
   if (IsMustTail) {
     // Force this to be a tail call.  The verifier rules are enough to ensure
     // that we can lower this successfully without moving the return address
-    // around.
+    // around. User should be aware of lazy dynamic linking issue in bug 15086.
     isTailCall = true;
   } else if (isTailCall) {
     // Check if it's really possible to do a tail call.
Index: test/CodeGen/X86/pic.ll
===================================================================
--- test/CodeGen/X86/pic.ll
+++ test/CodeGen/X86/pic.ll
@@ -196,9 +196,11 @@
 ; LINUX-NEXT: .LJTI7_0:
 ; LINUX:   .long	 .LBB7_2 at GOTOFF
 ; LINUX:   .long	 .LBB7_8 at GOTOFF
-; LINUX:   .long	 .LBB7_14 at GOTOFF
-; LINUX:   .long	 .LBB7_9 at GOTOFF
-; LINUX:   .long	 .LBB7_10 at GOTOFF
+; LINUX:   .long	 .LBB7_4 at GOTOFF
+; LINUX:   .long	 .LBB7_6 at GOTOFF
+; LINUX:   .long	 .LBB7_5 at GOTOFF
+; LINUX:   .long	 .LBB7_8 at GOTOFF
+; LINUX:   .long	 .LBB7_7 at GOTOFF
 }
 
 declare void @foo1(...)
Index: test/CodeGen/X86/tail-call-got.ll
===================================================================
--- test/CodeGen/X86/tail-call-got.ll
+++ test/CodeGen/X86/tail-call-got.ll
@@ -5,18 +5,16 @@
 
 define double @test1(double %x) nounwind readnone {
 ; CHECK-LABEL: test1:
-; CHECK: movl foo at GOT
-; CHECK-NEXT: jmpl
+; CHECK:  calll foo at PLT
   %1 = tail call double @foo(double %x) nounwind readnone
   ret double %1
 }
 
 declare double @foo(double) readnone
 
 define double @test2(double %x) nounwind readnone {
 ; CHECK-LABEL: test2:
-; CHECK: movl sin at GOT
-; CHECK-NEXT: jmpl
+; CHECK:  calll sin at PLT
   %1 = tail call double @sin(double %x) nounwind readnone
   ret double %1
 }
Index: test/CodeGen/X86/tailcallpic1.ll
===================================================================
--- test/CodeGen/X86/tailcallpic1.ll
+++ test/CodeGen/X86/tailcallpic1.ll
@@ -9,5 +9,5 @@
 entry:
 	%tmp11 = tail call fastcc i32 @tailcallee( i32 %in1, i32 %in2, i32 %in1, i32 %in2 )		; <i32> [#uses=1]
 	ret i32 %tmp11
-; CHECK: jmp tailcallee
+; CHECK: calll tailcallee
 }
Index: test/CodeGen/X86/tailcallpic2.ll
===================================================================
--- test/CodeGen/X86/tailcallpic2.ll
+++ test/CodeGen/X86/tailcallpic2.ll
@@ -9,7 +9,6 @@
 entry:
 	%tmp11 = tail call fastcc i32 @tailcallee( i32 %in1, i32 %in2, i32 %in1, i32 %in2 )		; <i32> [#uses=1]
 	ret i32 %tmp11
-; CHECK: movl tailcallee at GOT
-; CHECK: jmpl
+; CHECK: calll tailcallee at PLT
 }

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