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PL/I and C/C++ Compilers Step Up to Improve Performance on zEC12


Even as hardware moves toward ever-increasing parallelism to keep strong performance gains flowing, the other partner for application performance—the programming languages and compilers—have to step up to make the gains even stronger.

The latest Enterprise PL/I and XL C/C++ compilers have stepped up to the plate to leverage the new instructions in the zEnterprise EC12 (zEC12). By upgrading the compilers, applications can take full advantage of the zEC12 hardware with increased performance, both automatically and through recoding to exploit new built-in functions.

PL/I on zEC12

The Enterprise PL/I for z/OS V4R3 compiler exploits zEC12 hardware through the addition of the ARCHITECTURE(10) option. This option enables the use of new instructions such as the Decimal-Floating-Point Zoned-Conversion Facility and tuning of the compiler-generated code.

For many years, instructions have existed to convert zoned decimal to packed decimal and from packed decimal to zoned decimal. However, some of these instructions are slow. In addition, because packed decimals cannot be held in registers, optimization is hindered.

The Decimal-Floating-Point Zoned-Conversion Facility adds a new set of instructions that converts between decimal-floating-point (DFP) and zoned decimal. The usefulness of these new instructions seems limited because only a few organizations currently use DFP. However, the compiler can exploit these instructions even in programs that don’t use floating-point data.

In PL/I, zoned decimal is represented by the PICTURE data type; floating-point data is represented by the FLOAT data type.

Converting PICTURE to DFP

The new instructions in the Decimal-Floating-Point Zoned-Conversion Facility will help in programs that use PICTURE and DFP data. For instance, to convert PICTURE to DFP in the following example, the results are different for the ARCH(9) and ARCH(10) options.

*process float(dfp);

 pic2dfp: proc( ein, aus ) options(nodescriptor);

   dcl ein(0:100_000) pic'(9)9' connected;
   dcl aus(0:hbound(ein)) float dec(16) connected;
   dcl jx  fixed bin(31);

   do jx = lbound(ein) to hbound(ein);
     aus(jx) = ein(jx);
   end;
 end; 

Under ARCH(9), the loop consists the following 17 instructions: 

0060	F248	D0F0  	F000	PACK   	#pd580_1(5,r13,240),_shadow4(9,r15,0)
0066  	C050	0000  	0035   	LARL   	r5,F'53'
006C 	D204	D0F8  	D0F0	MVC   	#pd581_1(5,r13,248),#pd580_1(r13,240)
0072 	41F0	F009           LA     	r15,#AMNESIA(,r15,9)
0076  	D100	D0FC  	500C   	MVN   	#pd581_1(1,r13,252),+CONSTANT_AREA(r5,12)
007C  	D204  	D0E0  	D0F8   	MVC    	_temp2(5,r13,224),#pd581_1(r13,248)
0082  	F874  	D100  	2000   	ZAP    	#pd586_1(8,r13,256),_shadow3(5,r2,0)
0088  	D207  	D0E8  	D100   	MVC    	_temp1(8,r13,232),#pd586_1(r13,256)
008E  	5800  	4000          	L      	r0,_shadow2(,r4,0)
0092  	5850  	4004          	L      	r5,_shadow2(,r4,4)
0096  	EB00  	0020  	000D   	SLLG   	0,r0,32
009C  	1605                  	OR     	r0,r5
009E  	B3F3  	0000          	CDSTR	f0,r0
00A2  	EB00  	0020  	000C  	SRLG	r0,r0,32
00A8  	B914  	0011           LGFR	r1,r1
00AC  	B3F6  	0001           IEDTR	f0,f0,r1
00B0  	6000  	E000           STD	f0,_shadow1(,r14,0) 

Under ARCH(10), the loop consists of only the following eight instructions and runs more than four times faster:

0060  	EB2F  	0003  	00DF	SLLK	r2,r15,3
0066  	B9FA 	202F           ALRK	r2,r15,r2
006A 	A7FA 	0001           AHI    	r15,H'1'
006E  	B9FA 	2023          	ALRK	r2,r3,r2
0072  	ED08  	2000  	00AA	CDZT	f0,#AddressShadow(9,r2,0),b'0000'
0078  	B914  	0000           LGFR 	r0,r0
007C  	B3F6 	0000           IEDTR	f0,f0,r0
0080  	6001  	E000           STD    	f0,_shadow1(r1,r14,0) 

Melanie Ullmer is a senior development manager within IBM’s compiler team with responsibilities in the development of the COBOL, PL/I, C/C++ and Fortran languages and products.

Peter Elderon is a senior technical staff manager and the architect for PL/I across all IBM platforms.

Rajan Bhakta is the technical architect for IBM z/OS XL C/C++ compilers with six years of development experience for IBM XL C. He is the ISO C Standards representative for Canada, and the C representative for IBM in INCITS.

Visda Vokhshoori is a staff software developer in Compiler Development—Optimization and Code Generation team. She leads the effort of supporting transactional memory in IBM XL C/C++ on System z platform.

Yvonne Ma is a staff information developer with IBM Rational Software.


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