x86 compiler should handle the "div/rem by 1" case

The current implementation of the (div/rem)/imm algorithm in
ART's x86 compiler (X86Mir2Lir::GenDivRemLit) handles the only
case when imm == -1, imm >= 2 and imm <= -2, but in the case
when imm == 1, the result of calculation is incorrect.

This patch adds handler of the "div/rem by 1" case.

Change-Id: I4bcdcd9c17f5ccb6c60e7c359c00e04cd07f5bee
Signed-off-by: Alexei Zavjalov <alexei.zavjalov@intel.com>

1 files changed, 14 insertions, 4 deletions

diff --git a/compiler/dex/quick/x86/int_x86.cc b/compiler/dex/quick/x86/int_x86.cc
index 9dd6116..1df9254 100644
--- a/compiler/dex/quick/x86/int_x86.cc
+++ b/compiler/dex/quick/x86/int_x86.cc
@@ -456,10 +456,20 @@ RegLocation X86Mir2Lir::GenDivRemLit(RegLocation rl_dest, RegLocation rl_src,
   RegLocation rl_result = {kLocPhysReg, 0, 0, 0, 0, 0, 0, 0, 1, kVectorNotUsed,
                           r2, INVALID_REG, INVALID_SREG, INVALID_SREG};
 
-  // handle 0x80000000 / -1 special case.
-  LIR *minint_branch = 0;
-  if (imm == -1) {
+  // handle div/rem by 1 special case.
+  if (imm == 1) {
     if (is_div) {
+      // x / 1 == x.
+      StoreValue(rl_result, rl_src);
+    } else {
+      // x % 1 == 0.
+      LoadConstantNoClobber(r0, 0);
+      // For this case, return the result in EAX.
+      rl_result.low_reg = r0;
+    }
+  } else if (imm == -1) {  // handle 0x80000000 / -1 special case.
+    if (is_div) {
+      LIR *minint_branch = 0;
       LoadValueDirectFixed(rl_src, r0);
       OpRegImm(kOpCmp, r0, 0x80000000);
       minint_branch = NewLIR2(kX86Jcc8, 0, kX86CondEq);
@@ -479,7 +489,7 @@ RegLocation X86Mir2Lir::GenDivRemLit(RegLocation rl_dest, RegLocation rl_src,
     // For this case, return the result in EAX.
     rl_result.low_reg = r0;
   } else {
-    DCHECK(imm <= -2 || imm >= 2);
+    CHECK(imm <= -2 || imm >= 2);
     // Use H.S.Warren's Hacker's Delight Chapter 10 and
     // T,Grablund, P.L.Montogomery's Division by invariant integers using multiplication.
     int magic, shift;