[IfConversion] Correctly handle cases where analyzeBranch fails.

If analyzeBranch fails, on some targets, the out parameters point to
some blocks in the function. But we can't use that information, so make
sure to clear it out.  (In some places in IfConversion, we assume that
any block with a TrueBB is analyzable.)

The change to the testcase makes it trigger a bug on builds without this
fix: IfConvertDiamond tries to perform a followup "merge" operation,
which isn't legal, and we somehow end up with a branch to a deleted MBB.
I'm not sure how this doesn't crash the compiler.

Differential Revision: https://reviews.llvm.org/D67306

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@371434 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/CodeGen/IfConversion.cpp b/lib/CodeGen/IfConversion.cpp
index be30ad3001642d98e70443b26f2f415cb96efb41..99f59f2f946af4182c93ab053ca368cc0799cabb 100644 (file)
--- a/lib/CodeGen/IfConversion.cpp
+++ b/lib/CodeGen/IfConversion.cpp
@@ -912,6 +912,12 @@ void IfConverter::AnalyzeBranches(BBInfo &BBI) {
   BBI.BrCond.clear();
   BBI.IsBrAnalyzable =
       !TII->analyzeBranch(*BBI.BB, BBI.TrueBB, BBI.FalseBB, BBI.BrCond);
+  if (!BBI.IsBrAnalyzable) {
+    BBI.TrueBB = nullptr;
+    BBI.FalseBB = nullptr;
+    BBI.BrCond.clear();
+  }
+
   SmallVector<MachineOperand, 4> RevCond(BBI.BrCond.begin(), BBI.BrCond.end());
   BBI.IsBrReversible = (RevCond.size() == 0) ||
       !TII->reverseBranchCondition(RevCond);

diff --git a/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir b/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir
index 576362184031b185718978311b4cbbdb136f0289..a2218b149f1b8ba76c0cd0866f03253e1e16c5e5 100644 (file)
--- a/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir
+++ b/test/CodeGen/ARM/ifcvt-diamond-unanalyzable-common.mir
@@ -1,4 +1,4 @@
-# RUN: llc %s -o - -run-pass=if-converter | FileCheck %s
+# RUN: llc %s -o - -run-pass=if-converter -verify-machineinstrs | FileCheck %s
 # Make sure we correctly if-convert blocks containing an INLINEASM_BR.
 # CHECK: t2CMPri killed renamable $r2, 34
 # CHECK-NEXT: $r0 = t2MOVi 2, 1, $cpsr, $noreg
@@ -48,9 +48,8 @@ body:             |
     t2B %bb.3, 14, $noreg
   
   bb.3:
-    successors: %bb.4(0x80000000)
-  
     INLINEASM &"", 1
+    $sp = t2LDMIA_RET $sp, 14, $noreg, def $r4, def $pc
   
   bb.4.l_yes (address-taken):
     $sp = t2LDMIA_RET $sp, 14, $noreg, def $r4, def $pc