SimplifyCFG: fix a bug in switch to table conversion

We use gep to access the global array "switch.table", and the table index
should be treated as unsigned. When the highest bit is 1, this commit
zero-extends the index to an integer type with larger size.

For a switch on i2, we used to generate:
%switch.tableidx = sub i2 %0, -2
getelementptr inbounds [4 x i64]* @switch.table, i32 0, i2 %switch.tableidx

It is incorrect when %switch.tableidx is 2 or 3. The fix is to generate
%switch.tableidx = sub i2 %0, -2
%switch.tableidx.zext = zext i2 %switch.tableidx to i3
getelementptr inbounds [4 x i64]* @switch.table, i32 0, i3 %switch.tableidx.zext

rdar://17735071

llvm-svn: 213815

1 files changed, 41 insertions, 0 deletions

diff --git a/llvm/test/Transforms/SimplifyCFG/switch-table-bug.ll b/llvm/test/Transforms/SimplifyCFG/switch-table-bug.ll
new file mode 100644
index 00000000000..d2e19075935
--- /dev/null
+++ b/llvm/test/Transforms/SimplifyCFG/switch-table-bug.ll
@@ -0,0 +1,41 @@
+; RUN: opt -S -simplifycfg < %s | FileCheck %s
+; rdar://17735071
+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-darwin12.0.0"
+
+; When tableindex can't fit into i2, we should extend the type to i3.
+; CHECK-LABEL: @_TFO6reduce1E5toRawfS0_FT_Si
+; CHECK: entry:
+; CHECK-NEXT: sub i2 %0, -2
+; CHECK-NEXT: zext i2 %switch.tableidx to i3
+; CHECK-NEXT: getelementptr inbounds [4 x i64]* @switch.table, i32 0, i3 %switch.tableidx.zext
+; CHECK-NEXT: load i64* %switch.gep
+; CHECK-NEXT: ret i64 %switch.load
+define i64 @_TFO6reduce1E5toRawfS0_FT_Si(i2) {
+entry:
+  switch i2 %0, label %1 [
+    i2 0, label %2
+    i2 1, label %3
+    i2 -2, label %4
+    i2 -1, label %5
+  ]
+
+; <label>:1                                       ; preds = %entry
+  unreachable
+
+; <label>:2                                       ; preds = %2
+  br label %6
+
+; <label>:3                                       ; preds = %4
+  br label %6
+
+; <label>:4                                       ; preds = %6
+  br label %6
+
+; <label>:5                                       ; preds = %8
+  br label %6
+
+; <label>:6                                      ; preds = %3, %5, %7, %9
+  %7 = phi i64 [ 3, %5 ], [ 2, %4 ], [ 1, %3 ], [ 0, %2 ]
+  ret i64 %7
+}