Fix PR6300.

A virtual register can be used before it is defined in the same MBB if the MBB
is part of a loop. Teach the implicit-def pass about this case.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@96279 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 82 insertions, 3 deletions

diff --git a/lib/CodeGen/ProcessImplicitDefs.cpp b/lib/CodeGen/ProcessImplicitDefs.cpp
index e3df2e42cf..d7179b3e59 100644
--- a/lib/CodeGen/ProcessImplicitDefs.cpp
+++ b/lib/CodeGen/ProcessImplicitDefs.cpp
@@ -205,10 +205,9 @@ bool ProcessImplicitDefs::runOnMachineFunction(MachineFunction &fn) {
       // Process each use instruction once.
       for (MachineRegisterInfo::use_iterator UI = mri_->use_begin(Reg),
              UE = mri_->use_end(); UI != UE; ++UI) {
-        MachineInstr *RMI = &*UI;
-        MachineBasicBlock *RMBB = RMI->getParent();
-        if (RMBB == MBB)
+        if (UI.getOperand().isUndef())
           continue;
+        MachineInstr *RMI = &*UI;
         if (ModInsts.insert(RMI))
           RUses.push_back(RMI);
       }
diff --git a/test/CodeGen/X86/2010-02-15-ImplicitDefBug.ll b/test/CodeGen/X86/2010-02-15-ImplicitDefBug.ll
new file mode 100644
index 0000000000..c429172852
--- /dev/null
+++ b/test/CodeGen/X86/2010-02-15-ImplicitDefBug.ll
@@ -0,0 +1,80 @@
+; RUN: llc < %s > %t
+; PR6300
+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-f80:32:32-n8:16:32"
+target triple = "i386-pc-linux-gnu"
+
+; When the "154" loops back onto itself, it defines a register after using it.
+; The first value of the register is implicit-def.
+
+%"struct location_chain_def" = type { %"struct location_chain_def"*, %"struct rtx_def"*, %"struct rtx_def"*, i32 }
+%"struct real_value" = type { i32, [5 x i32] }
+%"struct rtx_def" = type { i16, i8, i8, %"union u" }
+%"union u" = type { %"struct real_value" }
+
+define i32 @variable_union(i8** nocapture %slot, i8* nocapture %data) nounwind {
+entry:
+  br i1 undef, label %"4.thread", label %"3"
+
+"4.thread":                                       ; preds = %entry
+  unreachable
+
+"3":                                              ; preds = %entry
+  br i1 undef, label %"19", label %"20"
+
+"19":                                             ; preds = %"3"
+  unreachable
+
+"20":                                             ; preds = %"3"
+  br i1 undef, label %"56.preheader", label %dv_onepart_p.exit
+
+dv_onepart_p.exit:                                ; preds = %"20"
+  unreachable
+
+"56.preheader":                                   ; preds = %"20"
+  br label %"56"
+
+"50":                                             ; preds = %"57"
+  br label %"56"
+
+"56":                                             ; preds = %"50", %"56.preheader"
+  br i1 undef, label %"57", label %"58"
+
+"57":                                             ; preds = %"56"
+  br i1 undef, label %"50", label %"58"
+
+"58":                                             ; preds = %"57", %"56"
+  br i1 undef, label %"62", label %"63"
+
+"62":                                             ; preds = %"58"
+  unreachable
+
+"63":                                             ; preds = %"58"
+  br i1 undef, label %"67", label %"66"
+
+"66":                                             ; preds = %"63"
+  br label %"67"
+
+"67":                                             ; preds = %"66", %"63"
+  br label %"68"
+
+"68":                                             ; preds = %"161", %"67"
+  br i1 undef, label %"153", label %"161"
+
+"153":                                            ; preds = %"68"
+  br i1 undef, label %"160", label %bb.nph46
+
+bb.nph46:                                         ; preds = %"153"
+  br label %"154"
+
+"154":                                            ; preds = %"154", %bb.nph46
+  %0 = phi %"struct location_chain_def"** [ undef, %bb.nph46 ], [ %1, %"154" ] ; <%"struct location_chain_def"**> [#uses=1]
+  %1 = bitcast i8* undef to %"struct location_chain_def"** ; <%"struct location_chain_def"**> [#uses=1]
+  store %"struct location_chain_def"* undef, %"struct location_chain_def"** %0, align 4
+  br i1 undef, label %"160", label %"154"
+
+"160":                                            ; preds = %"154", %"153"
+  br label %"161"
+
+"161":                                            ; preds = %"160", %"68"
+  br label %"68"
+}